机械设计 外文翻译

Numerical control technology and equipping development trend and countermeasure Equip the engineering level, level of determining the whole national economy of the modernized degree and modernized degree of industry, numerical control technolo gy is it develop new developing new high-tech industry and most advanced industr y to equip (such as information technology and his industry, biotechnology and his industry, aviation, spaceflight, etc. national defense industry) last technology and get ting more basic most equipment. Marx has ever said "the differences of different e conomic times, do not lie in what is produced, and lie in how to produce, produce with some means of labor ". Manufacturing technology and equipping the most ba sic means of production that are that the mankind produced the activity, and nume rical control technology is nowadays advanced manufacturing technology and equips the most central technology. Nowadays the manufacturing industry all around the world adopts numerical control technology extensively, in order to improve manufact uring capacity and level, improve the adaptive capacity and competitive power to th e changeable market of the trends. In addition every industrially developed country in the world also classifies the technology and numerical control equipment of num erical control as the strategic materials of the country, not merely take the great m easure to develop one's own numerical control technology and industry, and imple ment blockading and restrictive policy to our country in view of " high-grade, precisi on and advanced key technology of numerical control " and equipping. In a word, develop the advanced manufacturing technology taking numerical control technology as the core and already become every world developed country and accelerate ec onomic development in a more cost-effective manner, important way to improve the overall national strength and national position.

Numerical control technology is the technology controlled to mechanical movement and working course with digital information, integrated products of electromechanics that the numerical control equipment is the new technology represented by numeri cal control technology forms to the manufacture industry of the tradition and infiltrati on of the new developing manufacturing industry, namely the so-called digitization i s equipped, its technological range covers a lot of fields: (1)Mechanical manufacturi ng technology; (2)Information processing, processing, transmission technology; (3)Au tomatic control technology; (4)Servo drive technology; (5)Technology of the sensor;

(6)Software engineering ,etc..

Development trend of a numerical control technology

The application of numerical control technology has not only brought the revolutiona ry change to manufacturing industry of the tradition, make the manufacturing industr y become the industrialized symbol , and with the constant development of numeric al control technology and enlargement of the application, the development of some important trades (IT , automobile , light industry , medical treatment ,etc. ) to the n ational economy and the people's livelihood of his plays a more and more importan t role, because the digitization that these trades needed to equip has already been the main trend of modern development. Numerical control technology in the world

at present and equipping the development trend to see, there is the following sever al respect [1- ] in its main research focus.

1 A high-speed, high finish machining technology and new trend equipped

The efficiency, quality are subjavanufacturing technology. High-speed, high finish ma chining technology can raise the efficiency greatly , improve the quality and grade of the products, shorten production cycle and improve the market competitive powe r. Japan carries the technological research association first to classify it as one of t he 5 great modern manufacturing technologies for this, learn (CIRP) to confirm it a s the centre in the 21st century and study one of the directions in international pro duction engineering.

In the field of car industry, produce one second when beat such as production of 300,000 / vehicle per year, and many variety process it is car that equip key probl em that must be solved one of; In the fields of aviation and aerospace industry, sp are parts of its processing are mostly the thin wall and thin muscle, rigidity is very bad, the material is aluminium or aluminium alloy, only in a situation that cut the speed and cut strength very small high, could process these muscles, walls. Adopt large-scale whole aluminium alloy method that blank " pay empty " make the wing recently, such large-scale parts as the fuselage ,etc. come to substitute a lot of p arts to assemble through numerous rivet , screw and other connection way, make t he intensity , rigidity and dependability of the component improved. All these, to pr ocessing and equipping the demand which has proposed high-speed, high precise and high flexibility.

According to EMO2001 exhibition situation, high-speed machining center is it give s peed can reach 80m/min is even high , air transport competent speed can up to 1 00m/min to be about to enter. A lot of automobile factories in the world at present, including Shanghai General Motors Corporation of our country, have already adopt ed and substituted and made the lathe up with the production line part that the hig h-speed machining center makes up. HyperMach lathe of U.S.A. CINCINNATI Com pany enters to nearly biggest 60m/min of speed, it is 100m/min to be fast, the acc eleration reaches 2g, the rotational speed of the main shaft has already reached 6 0 000r/min. Processing a thin wall of plane parts, spend 30min only, and same par t general at a high speed milling machine process and take 3h, the ordinary milling machine is being processed to need 8h; The speed and acceleration of main shaf t of dual main shaft lathes of Germany DMG Company are up to 120000r/mm and 1g.

In machining accuracy, the past 10 years, ordinary progression accuse of machinin g accuracy of lathe bring 5μm up to from 10μm already, accurate grades of machi ning center from 3～5μm, rise to 1～1.5μm, and ultraprecision machining accuracy i s it enter nanometer grade to begin already (0.01μm).

In dependability, MTBF value of the foreign numerical control device has already re ached above 6 000h, MTBF value of the servo system reaches above 30000h, de monstrate very high dependability .

In order to realize high-speed, high finish machining, if the part of function related t o it is electric main shaft, straight line electrical machinery get fast development, th

e application is expanded further .

1.2 Link and process and compound to process the fast development of the lathe i n 5 axes

Adopt 5 axles to link the processing of the three-dimensional curved surface part, c an cut with the best geometry form of the cutter , not only highly polished, but als o efficiency improves by a large margin . It is generally acknowledged, the efficienc y of an 5 axle gear beds can equal 2 3 axle gear beds, is it wait for to use the c ubic nitrogen boron the milling cutter of ultra hard material is milled and pared at a high speed while quenching the hard steel part, 5 axles link and process 3 const ant axles to link and process and give play to higher benefit. Because such reason s as complicated that 5 axles link the numerical control system , host computer str ucture that but go over, it is several times higher that its price links the numerical control lathe than 3 axles , in addition the technological degree of difficulty of progr amming is relatively great, have restricted the development of 5 axle gear beds.

At present because of electric appearance of main shaft, is it realize 5 axle compl ex main shaft hair structure processed to link greatly simplify to make, it makes de gree of difficulty and reducing by a large margin of the cost, the price disparity of the numerical control system shrinks. So promoted 5 axle gear beds of head of co mplex main shaft and compound to process the development of the lathe (process the lathe including 5).

At EMO2001 exhibition, new Japanese 5 of worker machine process lathe adopt co mplex main shaft hair, can realize the processing of 4 vertical planes and processi ng of the wanton angle, make 5 times process and 5 axles are processed and ca n be realized on the same lathe, can also realize the inclined plane and pour the processing of the hole of awls. Germany DMG Company exhibits the DMUVoution series machining center, but put and insert and put processing and 5 axles 5 time s to link and process in once, can be controlled by CNC system or CAD/CAM is c ontrolled directly or indirectly.

1.3 Become the main trend of systematic development of contemporary numerical c ontrol intelligently, openly, networkedly.

The numerical control equipment in the 21st century will be sure the intelligent syst em, the intelligent content includes all respects in the numerical control system: It i s intelligent in order to pursue the efficiency of processing and process quality, con trol such as the self-adaptation of the processing course, the craft parameter is pro duced automatically; Join the convenient one in order to improve the performance of urging and use intelligently, if feedforward control , adaptive operation , electrical machinery of parameter , discern load select models , since exactly makes etc. a utomatically; The ones that simplified programming , simplified operating aspect are intelligent, for instance intelligent automatic programming , intelligent man-machine interface ,etc.; There are content of intelligence diagnose , intelligent monitoring , di agnosis convenient to be systematic and maintaining ,etc..

Produce the existing problem for the industrialization of solving the traditional nume rical control system sealing and numerical control application software. A lot of cou ntries carry on research to the open numerical control system at present, such as

NGC of U.S.A. (The Next Generation Work-Station/Machine Control), OSACA of Eu ropean Community (Open System Architecture for Control within Automation System s), OSEC (Open System Environment for Controller) of Japan, ONC (Open Numeri cal Control System) of China, etc.. The numerical control system melts to become the future way of the numerical control system open. The so-called open numerical control system is the development of the numerical control system can be on unifi ed operation platform, face the lathe producer and end user, through changing, incr easing or cutting out the structure target(numerical control function), form the serrati on, and can use users specially conveniently and the technical know-how is integra ted in the control system, realize the open numerical control system of different var iety , different grade fast, form leading brand products with distinct distinction. Syst em structure norm of the open numerical control system at present, communication norm , disposing norm , operation platform , numerical control systematic function storehouse and numerical control systematic function software development ,etc. are the core of present research.

The networked numerical control equipment is a new light spot of the fair of the in ternationally famous lathe in the past two years. Meeting production line , manufact ure system , demand for the information integration of manufacturing company netw orkedly greatly of numerical control equipment, realize new manufacture mode such as quick make , fictitious enterprise , basic Entrance that the whole world make t oo. Some domestic and international famous numerical control lathes and systemati c manufacturing companies of numerical control have all introduced relevant new c oncepts and protons of a machine in the past two years, if in EMO2001 exhibition, " Cyber Production Center " that the company exhibits of mountain rugged campst ool gram in Japan (Mazak) (intellectual central production control unit, abbreviated as CPC); The lathe company of Japanese big Wei (Okuma ) exhibits " IT plaza " (the information technology square , is abbreviated as IT square ); Open Manufactu ring Environment that the company exhibits of German Siemens (Siemens ) (open t he manufacturing environment, abbreviated as OME),etc., have reflected numerical control machine tooling to the development trend of networked direction.

1.4 Pay attention to the new technical standard, normal setting-up

1.4.1 Design the norm of developing about the numerical control system

As noted previously, there are better common ability, flexibility, adaptability, expandi ng in the open numerical control system, such countries as U.S.A. ,European Com munity and Japan ,etc. implement the strategic development plan one after another , carry on the research and formulation of the systematic norm (OMAC , OSACA , OSEC ) of numerical control of the open system structure, 3 biggest economies in the world have carried on the formulation that nearly the same science planned a nd standardized in a short time, have indicated a new arrival of period of change of numerical control technology. Our country started the research and formulation of standardizing the frame of ONC numerical control system of China too in 2000. 1.4.2 About the numerical control standard

The numerical control standard is a kind of trend of information-based development of manufacturing industry. Information exchange among 50 years after numerical c

ontrol technology was born was all because of ISO6983 standard, namely adopt G, M code describes how processes, its essential characteristic faces the processing course, obviously, he can't meet high-speed development of modern numerical cont rol technology's needs more and more already. For this reason, studying and maki ng a kind of new CNC system standard ISO14649 (STEP-NC) in the world, its pur pose is to offer a kind of neutral mechanism not depending on the concrete syste m, can describe the unified data model in cycle of whole life of the products, thus realize the whole manufacture process, standardization of and even each industrial field product information.

The appearance of STEP-NC may be a revolution of the technological field of the numerical control, on the development and even the whole manufacturing industry of numerical control technology, will exert a far-reaching influence. First of all, STE P-NC puts forward a kind of brand-new manufacture idea, in the traditional manufa cture idea, NC processes the procedures to all concentrate on individual computer. Under the new standard, NC procedure can be dispersed on Internet, this is exac tly a direction of open , networked development of numerical control technology. Se condly, STEP-NC numerical control system can also reduce and process the drawi ng (about 75%), process the procedure to work out the time (about 35%) and proc ess the time (about 50%) greatly.

At present, American-European countries pay much attention to the research of ST EP-NC, Europe initiates IMS plan (1999.1.1-2001.12.3) of STEP-NC. 20 CAD/CAM/ CAPP/CNC users, manufacturers and academic organizations from Europe and Jap an participated in this plan. STEP Tools Company of U.S.A. is a developer of the data interchange software of manufacturing industry in the global range, he has alr eady developed the super model (Super Model ) which accuses of information exc hange of machine tooling by counting, its goal is to describe all processing courses with the unified norm. Such new data interchange form has already been verified i n allocating the SIEMENS, FIDIA and European OSACA-NC numerical control at pr esent.

2 pairs of basic estimations of technology and industry development of numerical c ontrol of our country

The technology of numerical control of our country started in 1958, the developmen t course in the past 50 years can roughly be divided into 3 stages: The first stage is from 1958 to 1979, namely closed developing stage. In this stages, because te chnology of foreign countries blockade and basic restriction of terms of our country, the development of numerical control technology is comparatively slow. During "Six th Five-Year Plan Period" , " the Seventh Five-Year Plan Period " of the country in second stage and earlier stage in " the Eighth Five-Year Plan Period ", namely in troduce technology, digest and assimilate, the stage of establishing the system of p roduction domesticization arisesing tentatively. At this stage , because of reform an d opening-up and national attention , and study the improvement of the developme nt environment and international environment, research , development and all makin g considerable progress in production domesticization of the products of the technol ogy of numerical control of our country. The third stage is and during the "Ninth Fi

ve-Year Plan Period" on the later stage in "the Eighth Five-Year Plan Period" of th e country, namely implement the research of industrialization, enter market competit ion stage. At this stage, made substantive progress in industrialization of the dome stic numerical control equipment of our country. In latter stage for "the Ninth Five-Y ear Plan ", the domestic occupation rate of market of the domestic numerical contr ol lathe is up to 50%, it is up to 10% too to mix the domestic numerical control s ystem (popular).

Make a general survey of the development course in the past 50 years of technolo gy of numerical control of our country, especially through tackling key problems of

4 Five-Year Plans, all in all has made following achievements.

a. Have established the foundation of the technical development of numerical contr ol, has mastered modern numerical control technology basically. Our country has al ready, the numerical control host computer, basic technology of special plane and f ittings grasped and driven from the numerical control system and survey basically n ow, among them most technology have already possessed and commercialized the foundation developed, some technology has already, industrialization commercialize d.

b. Have formed the industrial base of numerical control tentatively. In tackling key problems the foundation that the achievement and some technology commercialize, set up the systematic factories of numerical control with production capacity in batc hes such as numerical control in Central China, numerical control of the spaceflight et

c.. Electrical machinery plant of Lanzhou, such factory and the first machine tool plant of Beijing , the first machine tool plant of Jinan ,etc. several numerical contr ol host computer factories of a batch of servo systems and servo electrical machin eries as the numerical control in Central China, etc.. These factories have formed t he numerical control industrial base of our country basically.

c. Have set up a numerical control research, development, managerial talent's basic team.

Though has made considerable progress in research and development and industri alization of numerical control technology, but we will realize soberly, the research a nd development of the technology of advanced numerical control of our country, es pecially there is greater disparity in current situation and current demand of our co untry of engineering level in industrialization. Though very fast from watching the d evelopment of our country vertically, have disparity horizontally more than (compare foreign countries with) not merely engineering level, there is disparity too in develo pment speed in some aspects, namely the engineering level disparity between som e high-grade , precision and advanced numerical control equipment has the tenden cy to expand . Watch from world, estimate roughly as follows about the engineerin g level of numerical control of our country and industrialization level.

a. On the engineering level, in probably backward 10-1 years with the advanced le vel in foreign countries, it is bigger in high-quality precision and sophisticated techn ology.

b. On the industrialization level, the occupation rate of market is low, the variety co verage rate is little, have not formed the large-scale production yet; The specialized

level of production of function part and ability of forming a complete set are relati vely low; Appearance quality is relatively poor; Dependability is not high, the comm ercialized degree is insufficient; One's own brand effect that the domestic numerical control system has not been set up yet, users have insufficient confidence.

c. On the ability of sustainable development, research and development of numeric al control technology, project ability is relatively weak to the competition; It is not st rong that the technological application of numerical control expands dynamics; Rese arch, formulation that relevant standards are normal lag behin

d.

It is analyzed that the main reason for having above-mentioned disparity has the fo llowing several respect.

a. Realize the respect. Know to industry's process arduousness , complexity and lo ng-term characteristic of domestic numerical control insufficiently; It is difficult to un derestimate to add strangling, system, etc. to the unstandard, foreign blockade of t he market; It is not enough to analyse to the technological application level and ab ility of numerical control of our country.

b. System. Pay close attention to numerical control industrialization many in the iss ue, consider numerical control industrialization little in the issue synthetically in term s of the systematic one, industry chain in terms of technology; Have not set up rel ated system, perfect training , service network of intact high quality ,et

c. and suppo rted the system.

c. Mechanism. It causes the brain drain, restraining technology and technological ro ute from innovating again, products innovation that the bad machine is made, and has restricted the effective implementation of planning, has often planned the ideal, implement the difficulty.

d. Technology. The autonomous innovation in technology of enterprises is indifferen t; the project of key technology is indifferent. The standard of the lathe lags behind, the level is relatively low, it is not enough for new standard of the numerical contr ol system to study.

3 pairs of strategic thinking of technology and industrialized development of numeri cal control of our country

3.1 Strategic consideration

Our country make big country, industry is it is it accept front instead of transformati on of back end to try one's best to want in shifting in world, namely should master and make key technology advanced, otherwise in a new round of international ind ustrial structure adjustment, the manufacturing industry of our country will step forw ard and " leave the core spaces ". We regard resource, environment , market as t he cost, it is only an international " machining center " in the new economic patter n of the world to exchange the possibility got and " assemble the centre ", but not master the position of the manufacturing center of key technology , will so influen ce the development process of the modern manufacturing industry of our country s eriously.

We should stand in the height of national security strategy paying attention to num erical control technology and industry's question , at first seen from social safety, b ecause manufacturing industry whether our country obtain employment most populo

us trade, the development of manufacturing industry not only can improve the peop le's living standard but also can alleviate the pressure of employment of our countr y , ensure the stability of the society; Secondly seen from national defense security, the western developed country has classified all the high-grade , precision and ad vanced numerical control products as the strategic materials of the country, realizin g the embargo and restriction to our country, " Toshiba incident " and " Cox Repor t " is the best illustration.

3.2 Development tactics

Proceed from the angles of the fundamental realities of the country of our country, regard the strategic demand of the country and market demand of national econo my as the direction, regard improving our country and making the comprehensive c ompetitive power of equipping industry and industrialization level as the goal, use t he systematic method , be able to choose to make key technology upgraded in de velopment of equipping industry and support technology supporting the development of industrialization in our country in initial stage of 21st century in leading factor, t he ability to supply the necessary technology realizes making the jump developmen t of the equipping industry as the content of research and development . Emphasize market demand is a direction, namely take terminal products of numeric al control as the core, with the complete machine (Such as the numerical control l athe having a large capacity and a wide range, milling machine, high speed high p recise high-performance numerical control lathe, digitized machinery of model, key i ndustry key equipment, etc.) drive the development of the numerical control industr y. Solve the numerical control system and relevant functions part especially The de pendability that (digitized servo system and electrical machinery, high speed electric main shaft system and new-enclosure that equip, etc.) and production scale questi on. There are no products that scale will not have high dependability; Will not hav

e cheap and products rich in the competitiveness without scale; Certainly, it is diffic ult to have day holding up one's head finally that there is no scale Chinese numeri cal control equipment.

In equiping researching and developing high-grade , precision and advancedly , sho uld emphasize the production, learning and research and close combination of the end user, regard " drawing, using, selling " as the goal, tackle key problems accor ding to the national will, in order to solve the needing badly of the country. Numerical control technology, emphasized innovation, put emphasis on researching and developing the technology and products with independent intellectual property ri ght before the competition, establish the foundation for the industry of numerical co ntrol of our country, sustainable development of equipment manufacture and even t he whole manufacturing industry.

数控技术和装备发展趋势及对策

装备工业的技术水平和现代化程度决定着整个国民经济的水平和现代化程度，数控技术及装备是发展新兴高新技术产业和尖端工业（如信息技术及其产业、生物技术及其产业、航空、航天等国防工业产业）的使能技术和最基本的装备。马克思曾经说过“各种经济时代的区别，不在于生产什么，而在于怎样生产，用什么劳动资料生产”。制造技术和装备就是人类生产

活动的最基本的生产资料，而数控技术又是当今先进制造技术和装备最为核心的技术。当今世界各国制造业广泛采用数控技术，以提高制造能力和水平，提高对动态多变市场的适应能力和竞争能力。此外，世界上各工业发达国家还将数控技术及数控装备列为国家的战略物资，不仅采取重大措施来发展自己的数控技术及其产业，而且在“高精尖”数控关键技术和装备方面对我国实行封锁和限制政策。总之，大力发展以数控技术为核心的先进制造技术已成为世界各发达国家加速经济发展、提高综合国力和国家地位的重要途径。

数控技术是用数字信息对机械运动和工作过程进行控制的技术，数控装备是以数控技术为代表的新技术对传统制造产业和新兴制造业的渗透形成的机电一体化产品，即所谓的数字化装备，其技术范围覆盖很多领域：(1)机械制造技术；(2)信息处理、加工、传输技术；(3)自动控制技术；(4)伺服驱动技术；(5)传感器技术；(6)软件技术等。

1 数控技术的发展趋势

数控技术的应用不但给传统制造业带来了革命性的变化，使制造业成为工业化的象征，而且随着数控技术的不断发展和应用领域的扩大，他对国计民生的一些重要行业（IT、汽车、轻工、医疗等）的发展起着越来越重要的作用，因为这些行业所需装备的数字化已是现代发展的大趋势。从目前世界上数控技术及其装备发展的趋势来看，其主要研究热点有以下几个方面［1～4］。

1.1 高速、高精加工技术及装备的新趋势

效率、质量是先进制造技术的主体。高速、高精加工技术可极大地提高效率，提高产品的质量和档次，缩短生产周期和提高市场竞争能力。为此日本先端技术研究会将其列为5大现代制造技术之一，国际生产工程学会（CIRP）将其确定为21世纪的中心研究方向之一。在轿车工业领域，年产30万辆的生产节拍是40秒/辆，而且多品种加工是轿车装备必须解决的重点问题之一；在航空和宇航工业领域，其加工的零部件多为薄壁和薄筋，刚度很差，材料为铝或铝合金，只有在高切削速度和切削力很小的情况下，才能对这些筋、壁进行加工。近来采用大型整体铝合金坯料“掏空”的方法来制造机翼、机身等大型零件来替代多个零件通过众多的铆钉、螺钉和其他联结方式拼装，使构件的强度、刚度和可靠性得到提高。这些都对加工装备提出了高速、高精和高柔性的要求。

从EMO2001展会情况来看，高速加工中心进给速度可达80m/min，甚至更高，空运行速度可达100m/min左右。目前世界上许多汽车厂，包括我国的上海通用汽车公司，已经采用以高速加工中心组成的生产线部分替代组合机床。美国CINCINNATI公司的HyperMach机床进给速度最大达60m/min，快速为100m/min，加速度达2g，主轴转速已达60 000r/mi n。加工一个薄壁飞机零件，只用30min，而同样的零件在一般高速铣床加工需3h，在普通铣床加工需8h；德国DMG公司的双主轴车床的主轴速度及加速度分别达120000r/mm和1g。

在加工精度方面，近10年来，普通级数控机床的加工精度已由10μm提高到5μm，精密级加工中心则从3～5μm，提高到1～1.5μm，并且超精密加工精度已开始进入纳米级(0.01μm)。

在可靠性方面，国外数控装置的MTBF值已达6 000h以上，伺服系统的MTBF值达到30 000h以上，表现出非常高的可靠性。

为了实现高速、高精加工，与之配套的功能部件如电主轴、直线电机得到了快速的发展，应用领域进一步扩大。

1.2 五轴联动加工和复合加工机床快速发展

采用5轴联动对三维曲面零件的加工，可用刀具最佳几何形状进行切削，不仅光洁度高，而且效率也大幅度提高。一般认为，1台5轴联动机床的效率可以等于2台3轴联动机床，特别是使用立方氮化硼等超硬材料铣刀进行高速铣削淬硬钢零件时，5轴联动加工可比3轴

联动加工发挥更高的效益。但过去因5轴联动数控系统、主机结构复杂等原因，其价格要比3轴联动数控机床高出数倍，加之编程技术难度较大，制约了5轴联动机床的发展。

当前由于电主轴的出现，使得实现5轴联动加工的复合主轴头结构大为简化，其制造难度和成本大幅度降低，数控系统的价格差距缩小。因此促进了复合主轴头类型5轴联动机床和复合加工机床（含5面加工机床）的发展。

在EMO2001展会上，新日本工机的5面加工机床采用复合主轴头，可实现4个垂直平面的加工和任意角度的加工，使得5面加工和5轴加工可在同一台机床上实现，还可实现倾斜面和倒锥孔的加工。德国DMG公司展出DMUVoution系列加工中心，可在一次装夹下实现5面加工和5轴联动加工，可由CNC系统控制或CAD/CAM直接或间接控制。

1.3 智能化、开放式、网络化成为当代数控系统发展的主要趋势

21世纪的数控装备将是具有一定智能化的系统，智能化的内容包括在数控系统中的各个方面：为追求加工效率和加工质量方面的智能化，如加工过程的自适应控制，工艺参数自动生成；为提高驱动性能及使用连接方便的智能化，如前馈控制、电机参数的自适应运算、自动识别负载自动选定模型、自整定等；简化编程、简化操作方面的智能化，如智能化的自动编程、智能化的人机界面等；还有智能诊断、智能监控方面的内容、方便系统的诊断及维修等。为解决传统的数控系统封闭性和数控应用软件的产业化生产存在的问题。目前许多国家对开放式数控系统进行研究，如美国的NGC(The Next Generation Work-Station/Machine Co ntrol)、欧共体的OSACA(Open System Architecture for Control within Automation Sys tems)、日本的OSEC(Open System Environment for Controller)，中国的ONC(Open N umerical Control System)等。数控系统开放化已经成为数控系统的未来之路。所谓开放式数控系统就是数控系统的开发可以在统一的运行平台上，面向机床厂家和最终用户，通过改变、增加或剪裁结构对象（数控功能），形成系列化，并可方便地将用户的特殊应用和技术诀窍集成到控制系统中，快速实现不同品种、不同档次的开放式数控系统，形成具有鲜明个性的名牌产品。目前开放式数控系统的体系结构规范、通信规范、配置规范、运行平台、数控系统功能库以及数控系统功能软件开发工具等是当前研究的核心。

网络化数控装备是近两年国际著名机床博览会的一个新亮点。数控装备的网络化将极大地满足生产线、制造系统、制造企业对信息集成的需求，也是实现新的制造模式如敏捷制造、虚拟企业、全球制造的基础单元。国内外一些著名数控机床和数控系统制造公司都在近两年推出了相关的新概念和样机，如在EMO2001展中，日本山崎马扎克（Mazak)公司展出的“Cy berProduction Center”（智能生产控制中心，简称CPC)；日本大隈（Okuma）机床公司展出“IT plaza”（信息技术广场，简称IT广场)；德国西门子(Siemens)公司展出的Open Ma nufacturing Environment（开放制造环境，简称OME）等，反映了数控机床加工向网络化方向发展的趋势。

1.4 重视新技术标准、规范的建立

1.4.1 关于数控系统设计开发规范

如前所述，开放式数控系统有更好的通用性、柔性、适应性、扩展性，美国、欧共体和日本等国纷纷实施战略发展计划，并进行开放式体系结构数控系统规范(OMAC、OSACA、OS EC)的研究和制定，世界3个最大的经济体在短期内进行了几乎相同的科学计划和规范的制定，预示了数控技术的一个新的变革时期的来临。我国在2000年也开始进行中国的ONC 数控系统的规范框架的研究和制定。

1.4.2 关于数控标准

数控标准是制造业信息化发展的一种趋势。数控技术诞生后的50年间的信息交换都是基于ISO6983标准，即采用G，M代码描述如何（how）加工，其本质特征是面向加工过程，显然，他已越来越不能满足现代数控技术高速发展的需要。为此，国际上正在研究和制定一

种新的CNC系统标准ISO14649（STEP－NC)，其目的是提供一种不依赖于具体系统的中性机制，能够描述产品整个生命周期内的统一数据模型，从而实现整个制造过程，乃至各个工业领域产品信息的标准化。

STEP-NC的出现可能是数控技术领域的一次革命，对于数控技术的发展乃至整个制造业，将产生深远的影响。首先，STEP-NC提出一种崭新的制造理念，传统的制造理念中，NC 加工程序都集中在单个计算机上。而在新标准下，NC程序可以分散在互联网上，这正是数控技术开放式、网络化发展的方向。其次，STEP-NC数控系统还可大大减少加工图纸（约75％）、加工程序编制时间（约35％）和加工时间（约50％）。

目前，欧美国家非常重视STEP-NC的研究，欧洲发起了STEP-NC的IMS计划(1999.1.1～2001.12.31)。参加这项计划的有来自欧洲和日本的20个CAD/CAM/CAPP/CNC用户、厂商和学术机构。美国的STEP Tools公司是全球范围内制造业数据交换软件的开发者，他已经开发了用作数控机床加工信息交换的超级模型(Super Model)，其目标是用统一的规范描述所有加工过程。目前这种新的数据交换格式已经在配备了SIEMENS、FIDIA以及欧洲OSACA-NC数控系统的原型样机上进行了验证。

2 对我国数控技术及其产业发展的基本估计

我国数控技术起步于1958年，近50年的发展历程大致可分为3个阶段：第一阶段从195 8年到1979年，即封闭式发展阶段。在此阶段，由于国外的技术封锁和我国的基础条件的限制，数控技术的发展较为缓慢。第二阶段是在国家的“六五”、“七五”期间以及“八五”的前期，即引进技术，消化吸收，初步建立起国产化体系阶段。在此阶段，由于改革开放和国家的重视，以及研究开发环境和国际环境的改善，我国数控技术的研究、开发以及在产品的国产化方面都取得了长足的进步。第三阶段是在国家的“八五”的后期和“九五”期间，即实施产业化的研究，进入市场竞争阶段。在此阶段，我国国产数控装备的产业化取得了实质性进步。在“九五”末期，国产数控机床的国内市场占有率达50％，配国产数控系统（普及型）也达到了10％。

纵观我国数控技术近50年的发展历程，特别是经过4个5年计划的攻关，总体来看取得了以下成绩。

a. 奠定了数控技术发展的基础，基本掌握了现代数控技术。我国现在已基本掌握了从数控系统、伺服驱动、数控主机、专机及其配套件的基础技术，其中大部分技术已具备进行商品化开发的基础，部分技术已商品化、产业化。

b. 初步形成了数控产业基地。在攻关成果和部分技术商品化的基础上，建立了诸如华中数控、航天数控等具有批量生产能力的数控系统生产厂。兰州电机厂、华中数控等一批伺服系统和伺服电机生产厂以及北京第一机床厂、济南第一机床厂等若干数控主机生产厂。这些生产厂基本形成了我国的数控产业基地。

c. 建立了一支数控研究、开发、管理人才的基本队伍。

虽然在数控技术的研究开发以及产业化方面取得了长足的进步，但我们也要清醒地认识到，我国高端数控技术的研究开发，尤其是在产业化方面的技术水平现状与我国的现实需求还有较大的差距。虽然从纵向看我国的发展速度很快，但横向比（与国外对比）不仅技术水平有差距，在某些方面发展速度也有差距，即一些高精尖的数控装备的技术水平差距有扩大趋势。从国际上来看，对我国数控技术水平和产业化水平估计大致如下。

a. 技术水平上，与国外先进水平大约落后10～15年，在高精尖技术方面则更大。

b. 产业化水平上，市场占有率低，品种覆盖率小，还没有形成规模生产；功能部件专业化生产水平及成套能力较低；外观质量相对差；可靠性不高，商品化程度不足；国产数控系统尚未建立自己的品牌效应，用户信心不足。

c. 可持续发展的能力上，对竞争前数控技术的研究开发、工程化能力较弱；数控技术应用

领域拓展力度不强；相关标准规范的研究、制定滞后。

分析存在上述差距的主要原因有以下几个方面。

a. 认识方面。对国产数控产业进程艰巨性、复杂性和长期性的特点认识不足；对市场的不规范、国外的封锁加扼杀、体制等困难估计不足；对我国数控技术应用水平及能力分析不够。

b. 体系方面。从技术的角度关注数控产业化问题的时候多，从系统的、产业链的角度综合考虑数控产业化问题的时候少；没有建立完整的高质量的配套体系、完善的培训、服务网络等支撑体系。

c. 机制方面。不良机制造成人才流失，又制约了技术及技术路线创新、产品创新，且制约了规划的有效实施，往往规划理想，实施困难。

d. 技术方面。企业在技术方面自主创新能力不强，核心技术的工程化能力不强。机床标准落后，水平较低，数控系统新标准研究不够。

3 对我国数控技术和产业化发展的战略思考

3.1 战略考虑

我国是制造大国，在世界产业转移中要尽量接受前端而不是后端的转移，即要掌握先进制造核心技术，否则在新一轮国际产业结构调整中，我国制造业将进一步“空芯”。我们以资源、环境、市场为代价，交换得到的可能仅仅是世界新经济格局中的国际“加工中心”和“组装中心”，而非掌握核心技术的制造中心的地位，这样将会严重影响我国现代制造业的发展进程。我们应站在国家安全战略的高度来重视数控技术和产业问题，首先从社会安全看，因为制造业是我国就业人口最多的行业，制造业发展不仅可提高人民的生活水平，而且还可缓解我国就业的压力，保障社会的稳定；其次从国防安全看，西方发达国家把高精尖数控产品都列为国家的战略物质，对我国实现禁运和限制，“东芝事件”和“考克斯报告”就是最好的例证。3.2 发展策略

从我国基本国情的角度出发，以国家的战略需求和国民经济的市场需求为导向，以提高我国制造装备业综合竞争能力和产业化水平为目标，用系统的方法，选择能够主导21世纪初期我国制造装备业发展升级的关键技术以及支持产业化发展的支撑技术、配套技术作为研究开发的内容，实现制造装备业的跨跃式发展。

强调市场需求为导向，即以数控终端产品为主，以整机（如量大面广的数控车床、铣床、高速高精高性能数控机床、典型数字化机械、重点行业关键设备等）带动数控产业的发展。重点解决数控系统和相关功能部件（数字化伺服系统与电机、高速电主轴系统和新型装备的附件等）的可靠性和生产规模问题。没有规模就不会有高可靠性的产品；没有规模就不会有价格低廉而富有竞争力的产品；当然，没有规模中国的数控装备最终难以有出头之日。

在高精尖装备研发方面，要强调产、学、研以及最终用户的紧密结合，以“做得出、用得上、卖得掉”为目标，按国家意志实施攻关，以解决国家之急需。

在竞争前数控技术方面，强调创新，强调研究开发具有自主知识产权的技术和产品，为我国数控产业、装备制造业乃至整个制造业的可持续发展奠定基础。

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机械设计理论 机械设计是一门通过设计新产品或者改进老产品来满足人类需求的应用技术科学。它涉及工程技术的各个领域，主要研究产品的尺寸、形状和详细结构的基本构思，还要研究产品在制造、销售和使用等方面的问题。 进行各种机械设计工作的人员通常被称为设计人员或者机械设计工程师。机械设计是一项创造性的工作。设计工程师不仅在工作上要有创造性，还必须在机械制图、运动学、工程材料、材料力学和机械制造工艺学等方面具有深厚的基础知识。如前所诉，机械设计的目的是生产能够满足人类需求的产品。发明、发现和科技知识本身并不一定能给人类带来好处，只有当它们被应用在产品上才能产生效益。因而，应该认识到在一个特定的产品进行设计之前，必须先确定人们是否需要这种产品。 应当把机械设计看成是机械设计人员运用创造性的才能进行产品设计、系统分析和制定产品的制造工艺学的一个良机。掌握工程基础知识要比熟记一些数据和公式更为重要。仅仅使用数据和公式是不足以在一个好的设计中做出所需的全部决定的。另一方面，应该认真精确的进行所有运算。例如，即使将一个小数点的位置放错，也会使正确的设计变成错误的。 一个好的设计人员应该勇于提出新的想法，而且愿意承担一定的风险，当新的方法不适用时，就使用原来的方法。因此，设计人员必须要有耐心，因为所花费的时间和努力并不能保证带来成功。一个全新的设计，要求屏弃许多陈旧的，为人们所熟知的方法。由于许多人墨守成规，这样做并不是一件容易的事。一位机械设计师应该不断地探索改进现有的产品的方法，在此过程中应该认真选择原有的、经过验证的设计原理，将其与未经过验证的新观念结合起来。 新设计本身会有许多缺陷和未能预料的问题发生，只有当这些缺陷和问题被解决之后，才能体现出新产品的优越性。因此，一个性能优越的产品诞生的同时，也伴随着较高的风险。应该强调的是，如果设计本身不要求采用全新的方法，就没有必要仅仅为了变革的目的而采用新方法。 在设计的初始阶段，应该允许设计人员充分发挥创造性，不受各种约束。即使产生了许多不切实际的想法，也会在设计的早期，即绘制图纸之前被改正掉。只有这样，才不致于堵塞创新的思路。通常，要提出几套设计方案，然后加以比较。很有可能在最后选定的方案中，采用了某些未被接受的方案中的一些想法。

土木工程外文文献翻译

专业资料 学院： 专业：土木工程 姓名： 学号： 外文出处：Structural Systems to resist (用外文写) Lateral loads 附件：1.外文资料翻译译文；2.外文原文。

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不是说富于想象力的结构设计就能够创造出伟大建筑。正相反，有许多例优美的建筑仅得到结构工程师适当的支持就被创造出来了，然而，如果没有天赋甚厚的建筑师的创造力的指导，那么，得以发展的就只能是好的结构，并非是伟大的建筑。无论如何，要想创造出高层建筑真正非凡的设计，两者都需要最好的。 虽然在文献中通常可以见到有关这七种体系的全面性讨论，但是在这里还值得进一步讨论。设计方法的本质贯穿于整个讨论。设计方法的本质贯穿于整个讨论中。 抗弯矩框架 抗弯矩框架也许是低，中高度的建筑中常用的体系，它具有线性水平构件和垂直构件在接头处基本刚接之特点。这种框架用作独立的体系，或者和其他体系结合起来使用，以便提供所需要水平荷载抵抗力。对于较高的高层建筑，可能会发现该本系不宜作为独立体系，这是因为在侧向力的作用下难以调动足够的刚度。 我们可以利用STRESS，STRUDL 或者其他大量合适的计算机程序进行结构分析。所谓的门架法分析或悬臂法分析在当今的技术中无一席之地，由于柱梁节点固有柔性，并且由于初步设计应该力求突出体系的弱点，所以在初析中使用框架的中心距尺寸设计是司空惯的。当然，在设计的后期阶段，实际地评价结点的变形很有必要。 支撑框架 支撑框架实际上刚度比抗弯矩框架强，在高层建筑中也得到更广泛的应用。这种体系以其结点处铰接或则接的线性水平构件、垂直构件和斜撑构件而具特色，它通常与其他体系共同用于较高的建筑，并且作为一种独立的体系用在低、中高度的建筑中。

毕业设计外文翻译资料

外文出处： 《Exploiting Software How to Break Code》By Greg Hoglund, Gary McGraw Publisher : Addison Wesley Pub Date : February 17, 2004 ISBN : 0-201-78695-8 译文标题： JDBC接口技术 译文： JDBC是一种可用于执行SQL语句的JavaAPI（ApplicationProgrammingInterface应用程序设计接口）。它由一些Java语言编写的类和界面组成。JDBC为数据库应用开发人员、数据库前台工具开发人员提供了一种标准的应用程序设计接口，使开发人员可以用纯Java语言编写完整的数据库应用程序。 一、ODBC到JDBC的发展历程 说到JDBC，很容易让人联想到另一个十分熟悉的字眼“ODBC”。它们之间有没有联系呢？如果有，那么它们之间又是怎样的关系呢？ ODBC是OpenDatabaseConnectivity的英文简写。它是一种用来在相关或不相关的数据库管理系统（DBMS）中存取数据的，用C语言实现的，标准应用程序数据接口。通过ODBCAPI，应用程序可以存取保存在多种不同数据库管理系统（DBMS）中的数据，而不论每个DBMS使用了何种数据存储格式和编程接口。 1．ODBC的结构模型 ODBC的结构包括四个主要部分：应用程序接口、驱动器管理器、数据库驱动器和数据源。应用程序接口：屏蔽不同的ODBC数据库驱动器之间函数调用的差别，为用户提供统一的SQL编程接口。 驱动器管理器：为应用程序装载数据库驱动器。 数据库驱动器：实现ODBC的函数调用，提供对特定数据源的SQL请求。如果需要，数据库驱动器将修改应用程序的请求，使得请求符合相关的DBMS所支持的文法。 数据源：由用户想要存取的数据以及与它相关的操作系统、DBMS和用于访问DBMS的网络平台组成。 虽然ODBC驱动器管理器的主要目的是加载数据库驱动器，以便ODBC函数调用，但是数据库驱动器本身也执行ODBC函数调用，并与数据库相互配合。因此当应用系统发出调用与数据源进行连接时，数据库驱动器能管理通信协议。当建立起与数据源的连接时，数据库驱动器便能处理应用系统向DBMS发出的请求，对分析或发自数据源的设计进行必要的翻译，并将结果返回给应用系统。 2．JDBC的诞生 自从Java语言于1995年5月正式公布以来，Java风靡全球。出现大量的用java语言编写的程序，其中也包括数据库应用程序。由于没有一个Java语言的API，编程人员不得不在Java程序中加入C语言的ODBC函数调用。这就使很多Java的优秀特性无法充分发挥，比如平台无关性、面向对象特性等。随着越来越多的编程人员对Java语言的日益喜爱，越来越多的公司在Java程序开发上投入的精力日益增加，对java语言接口的访问数据库的API 的要求越来越强烈。也由于ODBC的有其不足之处，比如它并不容易使用，没有面向对象的特性等等，SUN公司决定开发一Java语言为接口的数据库应用程序开发接口。在JDK1．x 版本中，JDBC只是一个可选部件，到了JDK1．1公布时，SQL类包（也就是JDBCAPI）

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本科毕业论文(设计) 外文翻译 学院：机电工程学院 专业：机械工程及自动化 姓名：高峰 指导教师：李延胜 2011年05 月10日 教育部办公厅 Failure Analysis，Dimensional Determination And

Analysis，Applications Of Cams INTRODUCTION It is absolutely essential that a design engineer know how and why parts fail so that reliable machines that require minimum maintenance can be designed．Sometimes a failure can be serious，such as when a tire blows out on an automobile traveling at high speed．On the other hand，a failure may be no more than a nuisance．An example is the loosening of the radiator hose in an automobile cooling system．The consequence of this latter failure is usually the loss of some radiator coolant，a condition that is readily detected and corrected．The type of load a part absorbs is just as significant as the magnitude．Generally speaking，dynamic loads with direction reversals cause greater difficulty than static loads，and therefore，fatigue strength must be considered．Another concern is whether the material is ductile or brittle．For example，brittle materials are considered to be unacceptable where fatigue is involved． Many people mistakingly interpret the word failure to mean the actual breakage of a part．However，a design engineer must consider a broader understanding of what appreciable deformation occurs．A ductile material，however will deform a large amount prior to rupture．Excessive deformation，without fracture，may cause a machine to fail because the deformed part interferes with a moving second part．Therefore，a part fails(even if it has not physically broken)whenever it no longer fulfills its required function．Sometimes failure may be due to abnormal friction or vibration between two mating parts．Failure also may be due to a phenomenon called creep，which is the plastic flow of a material under load at elevated temperatures．In addition，the actual shape of a part may be responsible for failure．For example，stress concentrations due to sudden changes in contour must be taken into account．Evaluation of stress considerations is especially important when there are dynamic loads with direction reversals and the material is not very ductile． In general，the design engineer must consider all possible modes of failure，which include the following． ——Stress ——Deformation ——Wear ——Corrosion ——Vibration ——Environmental damage ——Loosening of fastening devices

机械类外文翻译

机械类外文翻译 塑料注塑模具浇口优化 摘要:用单注塑模具浇口位置的优化方法，本文论述。该闸门优化设计的目的是最大限度地减少注塑件翘曲变形，翘曲，是因为对大多数注塑成型质量问题的关键，而这是受了很大的部分浇口位置。特征翘曲定义为最大位移的功能表面到表面的特征描述零件翘曲预测长度比。结合的优化与数值模拟技术，以找出最佳浇口位置，其中模拟armealing算法用于搜索最优。最后，通过实例讨论的文件，它可以得出结论，该方法是有效的。 注塑模具、浇口位臵、优化、特征翘曲变形关键词: 简介 塑料注射成型是一种广泛使用的，但非常复杂的生产的塑料产品，尤其是具有高生产的要求，严密性，以及大量的各种复杂形状的有效方法。质量ofinjection 成型零件是塑料材料，零件几何形状，模具结构和工艺条件的函数。注塑模具的一个最重要的部分主要是以下三个组件集:蛀牙，盖茨和亚军，和冷却系统。拉米夫定、Seow(2000)、金和拉米夫定(2002) 通过改变部分的尼斯达到平衡的腔壁厚度。在平衡型腔充填过程提供了一种均匀分布压力和透射电镜,可以极大地减少高温的翘曲变形的部分～但仅仅是腔平衡的一个重要影响因素的一部分。cially Espe,部分有其功能上的要求,其厚度通常不应该变化。 pointview注塑模具设计的重点是一门的大小和位臵,以及流道系统的大小和布局。大门的大小和转轮布局通常被认定为常量。相对而言,浇口位臵与水口大小布局也更加灵活,可以根据不同的零件的质量。 李和吉姆(姚开屏,1996a)称利用优化流道和尺寸来平衡多流道系统为multiple 注射系统。转轮平衡被形容为入口压力的差异为一多型腔模具用相同的蛀牙,也存

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毕业设计(论文)外文资料翻译 系：机械工程系 专业：土木工程 姓名： 学号： 外文出处：Design of prestressed (用外文写) concrete structures 附件： 1.外文资料翻译译文；2.外文原文。

附件1：外文资料翻译译文 8-2简支梁布局 一个简单的预应力混凝土梁由两个危险截面控制：最大弯矩截面和端截面。这两部分设计好之后，中间截面一定要单独检查，必要时其他部位也要单独调查。最大弯矩截面在以下两种荷载阶段为控制情况，即传递时梁受最小弯矩M G的初始阶段和最大设计弯矩M T时的工作荷载阶段。而端截面则由抗剪强度、支承垫板、锚头间距和千斤顶净空所需要的面积来决定。所有的中间截面是由一个或多个上述要求，根它们与上述两种危险截面的距离来控制。对于后张构件的一种常见的布置方式是在最大弯矩截面采用诸如I形或T形的截面，而在接近梁端处逐渐过渡到简单的矩形截面。这就是人们通常所说的后张构件的端块。对于用长线法生产的先张构件，为了便于生产，全部只用一种等截面，其截面形状则可以为I形、双T形或空心的。在第5 、 6 和7章节中已经阐明了个别截面的设计，下面论述简支梁钢索的总布置。 梁的布置可以用变化混凝土和钢筋的办法来调整。混凝土的截面在高度、宽度、形状和梁底面或者顶面的曲率方面都可以有变化。而钢筋只在面积方面有所变化，不过在相对于混凝土重心轴线的位置方面却多半可以有变化。通过调整这些变化因素，布置方案可能有许多组合，以适应不同的荷载情况。这一点是与钢筋混凝土梁是完全不同的，在钢筋混凝土梁的通常布置中，不是一个统一的矩形截面便是一个统一的T形，而钢筋的位置总是布置得尽量靠底面纤维。 首先考虑先张梁，如图 8-7，这里最好采用直线钢索，因为它们在两个台座之间加力比较容易。我们先从图（a）的等截面直梁的直线钢索开始讨论。这样的布置都很简单，但这样一来，就不是很经济的设计了，因为跨中和梁端的要求会产生冲突。通常发生在跨度中央的最大弯矩截面中的钢索，最好尽量放低，以便尽可能提供最大力臂而提供最大的内部抵制力矩。当跨度中央的梁自重弯矩M G相当大时，就可以把c.g.s布置在截面核心范围以下很远的地方，而不致在传递时在顶部纤维中引起拉应力。然而对于梁端截面却有一套完全不同的要求。由于在梁端没有外力矩，因为在最后的时刻，安排钢索要以c.g.s与 c.g.c在结束区段一致，如此同样地获得克服压力分配的方法。无论如何，如果张应力在最后不能承受，放置 c.g.s.

引进外资外文翻译资料

河南科技学院新科学院 2013届本科毕业生论文（设计） 英文文献及翻译 Foreign capital inflows and welfare in an economy with imperfect competition 学生姓名：王艳杰 所在院系：经济系 所学专业：国际经济与贸易 导师姓名：侯黎杰 完成时间：2013年4月15日

Foreign capital inflows and welfare in an economy with imperfect competition Abstract:This paper examines the resource allocational and welfare effects of exogenous inflows of foreign capital in a general-equilibrium model with oligopolistic competition and unemployment. Although the welfare impact for the short run is ambiguous and dependent upon the strength of excess profits and scale economies relative to unemployment in manufacturing, in the long run additional inflows of foreign capital always improve national welfare with capital mobility. Hence, attracting foreign capital remains a sound policy for economies characterized by imperfect competition, scale economies,and regional unemployment. Keywords: International capital mobility; Imperfect competition; Welfare 1.Introduction The welfare effects of exogenous inflows of foreign capital in the presence of trade restrictions have been extensively studied. Brecher and Diaz Alejandro (1977) show that when imports are subject to tariffs, an introduction of fo reign capital inflows accentuates the tariff distortion and hence reduces national welfare if the import-competing sector is relatively capital-intensive. In contrast, Dei (1985) shows that when imports are restricted by quotas,foreign capital inflows in the presence of foreign-owned capital always improve welfare by depressing the rental and so lowering the payments to existing foreign-owned capital. Recently, Neary (1981), using a common framework for both tariffs and quotas, obtains more general results of foreign capital inflows; the welfare effect of such inflows depends crucially on whether foreign-owned capital exists initially in the home country. In addition, Khan (1982) and Grinols (1991) have examined the effects of foreign capital inflows for a generalized Harris-Todaro economy under tariff protection. Khan finds that the result by Brecher and Diaz Alejandro is still valid even in the presence of unemployment, whereas Grinols argues that increased foreign capital need not be detrimental to welfare if the opportunity costs of labor are sufficiently low. Noteworthy is that the models used by these authors are all based upon the premise of perfect competition along with constant returns-to-scale technology. Although perfect competition serves as a useful assumption in crystallizing theoretical insights, it nevertheless fails to depict many of the real-world phenomena. The real-world economy is characterized, to a large extent, by imperfect competition and economies of scale. The policy implications of imperfect competition and economies

机械类毕业设计外文文献翻译

沈阳工业大学工程学院 毕业设计（论文）外文翻译 毕业设计（论文）题目：工具盒盖注塑模具设计 外文题目：Friction , Lubrication of Bearing 译文题目：轴承的摩擦与润滑 系（部）：机械系 专业班级：机械设计制造及其自动化0801 学生姓名：王宝帅 指导教师：魏晓波 2010年10 月15 日

外文文献原文： Friction , Lubrication of Bearing In many of the problem thus far , the student has been asked to disregard or neglect friction . Actually , friction is present to some degree whenever two parts are in contact and move on each other. The term friction refers to the resistance of two or more parts to movement. Friction is harmful or valuable depending upon where it occurs. friction is necessary for fastening devices such as screws and rivets which depend upon friction to hold the fastener and the parts together. Belt drivers, brakes, and tires are additional applications where friction is necessary. The friction of moving parts in a machine is harmful because it reduces the mechanical advantage of the device. The heat produced by friction is lost energy because no work takes place. Also , greater power is required to overcome the increased friction. Heat is destructive in that it causes expansion. Expansion may cause a bearing or sliding surface to fit tighter. If a great enough pressure builds up because made from low temperature materials may melt. There are three types of friction which must be overcome in moving parts: (1)starting, (2)sliding, and(3)rolling. Starting friction is the friction between two solids that tend to resist movement. When two parts are at a state of rest, the surface irregularities of both parts tend to interlock and form a wedging action. To produce motion in these parts, the wedge-shaped peaks and valleys of the stationary surfaces must be made to slide out and over each other. The rougher the two surfaces, the greater is starting friction resulting from their movement . Since there is usually no fixed pattern between the peaks and valleys of two mating parts, the irregularities do not interlock once the parts are in motion but slide over each other. The friction of the two surfaces is known as sliding friction. As shown in figure ,starting friction is always greater than sliding friction . Rolling friction occurs when roller devces are subjected to tremendous stress which cause the parts to change shape or deform. Under these conditions, the material in front of a roller tends to pile up and forces the object to roll slightly uphill. This changing of shape , known as deformation, causes a movement of molecules. As a result ,heat is produced from the added energy required to keep the parts turning and overcome friction. The friction caused by the wedging action of surface irregularities can be overcome