【正文】 scribe the performance or functionality. What the user must do instead is to model the object geometry in an appropriate format. Usually tie engineer who is designing a monly analyzed part or assembly can purchase analysis software to evaluate the design. It is only in the case of an unusual design or performance requirement, where offtheshelf software is not available, that the engineer must formulate a unique model. In this case, the engineer will usually derive a mathematical model in the form of equations using he laws of physics and write a program to read the design description and calculate te performance parameters. These monly available analysis modules read the design description and generate performance result in the form of numbers, graphs, charts, etc.An Example of Using CAD CAD, normally used in engineering departments, has drastically changed these departments. Drawing used to be made on paper with pencil or pen and drawing instruments. They were then copied, and the copies were sent to the floor for production. The originals were stored in large drawers. Even a small enterprise could have thousands of large blueprints on file. If changes were necessary, the engineer would get the original out of the file drawer, make the need for all of the physical storage of prints. The puter also allowed for rapid and easy print modifications. The engineer or designer first draws the part on the screen this part drawing is the actual part geometry. The sizes and location are all correct so that the information can be used later to create a program to machine the part. The engineer or designer first draws the part on the screen. This part drawing is the actual part geometry. The sizes and locations are all correct so that the information can be used later to create a program to machine the part. The designer must work closely with the manufacturing people to establish some standards for design. CAD allows different layers (or levels) to be created. This allows the designer to put different potions of the part geometry on different layers. For example, imagine a simple part that has a 1/2inch slot milled in it and four holes drilled through it. The designer would put the slot on one layer of the drawing and the holes on another layer. This will allow other software to take the part geometry form each layer and assign different tools to it. Think of different layers as different machining operation that would have different tool assigned to them. Layers are like transparency. If we put all of the total transparencies on top of each other, we see the total part. But we can still take any one transparency and isolate some of the part geometry. The CAD system will print the blueprint so it appears there is only one layer, or individual layers can be printed. The designer also dimensions the part. This is quite automatic. The designer chooses where he/she wants dimensions placed and the puter places the actual dimensions. Dimensions would be on a different layer than part geometry. The puter allows designs to be viewed and tested before the actual part is even manufactured. The part can be tested make sure it fits with any mating pars. CAD system can check for interference of parts, which can save a lot of wasted machining and development time. CAD systems can stresstest part to see if they will meet the strength requirements of the application. The graphics abilities of CAD system also allow 3D viewing of part from any angle. Integrated CAD The emphasis of the chapter is integrated CAD/CAM. The integration aspect is acplished when the design and analysis modules are united into one package. The design geometry entered by the designer can be used by the analysis programs and by the manufacturing, inspection, inventory, and other aspects of the product lift cycle. The manifestation of integrating software is recognized when the user can sit down at a puter terminal, design a part, view it on the screen, analyze it for design requirements, and hit the proverbial manufacturing button the keyboard to have the part automatically manufactured, inspected, and delivered. Various stages of integration do exist, but none is as plete as the example just mentioned. Integration implies automation. Automation implies that the hardware and software can create a CAD database and use it to analyze and manufacture the part totally automatically, with little or no human intervention. The question as to whether human intervention is advisable is still open. Certainly human intelligence is valuable in developing a design in geometry and functionality, recognizing certain patterns and shortings of products, and formulating manufacturing plans. It has been suggested that artificial intelligence (AI) techniques can substitute for much of the human design/manufacturing input. AI research has had success in the areas of pattern recognition, planning, natural language understanding, robotic control, fault diagnosis, and other applications. The most well recognize area of AI is the development of expert system. Expert systems simulate human expertise by storing a knowledge base of data about a specific domain. The architecture of an expert system is shown in Figure . The knowledge base contains knowledge about a specific problem domain and facts stating the problem. The inference engine is the program control which searches te facts about the problem to satisfy the knowledge base ad above the problem計(jì)算機(jī)輔助設(shè)計(jì)一個好的機(jī)械設(shè)計(jì)產(chǎn)品必須保證產(chǎn)品的部分或全部功能在產(chǎn)品壽命中能夠正確有效地實(shí)現(xiàn)。8051單片機(jī)實(shí)踐與應(yīng)用[M] ， 清華大學(xué)出版社。模擬電子技術(shù)基礎(chǔ)簡明教程[M],.[8]盧靜,陳非凡,張高飛,[J]，北京機(jī)械工業(yè)學(xué)院學(xué)報(bào)。直流電機(jī)PWM閉環(huán)調(diào)速系統(tǒng)[J]，青島大學(xué)學(xué)報(bào)。怎樣保護(hù)電動機(jī)[M],中國農(nóng)業(yè)機(jī)械出版社。[2]張毅坤，陳善久，裘雪紅。同時在這里，我要感謝我的導(dǎo)師石炳存老師和畢業(yè)設(shè)計(jì)過程中所有給我真誠幫助的老師和同學(xué)。此控制器具有節(jié)能、工作可靠等特點(diǎn)，基本符合了人們對電動自行車控制器的要求。剎車控制也采用實(shí)時響應(yīng)，一檢測到剎車信號，剎車燈亮，并將速度調(diào)到零。在上述保護(hù)方案中,電流保護(hù)和蓄電池欠壓保護(hù)采用非恢復(fù)性保護(hù), 一旦進(jìn)入保護(hù)狀態(tài), 就必須等排除故障、重新啟動單片機(jī)系統(tǒng)后, 才能恢復(fù)工作。第三章 系統(tǒng)軟件設(shè)計(jì)基于AT89C51單片機(jī)的需要，本設(shè)計(jì)用