This paper summarizes that CAD (Computer Aided Design) uses computers and their graphic devices to help designers with their design work. Cad for short. In engineering and product design, computers can help designers undertake tasks such as calculation, information storage and drawing. In design, computers are usually used to calculate, analyze and compare many different schemes to determine the best scheme; All kinds of design information, whether digital, literal or graphic, can be stored in the internal memory or external memory of the computer and can be quickly retrieved; Designers usually start with sketches, and the heavy work of turning sketches into working drawings can be handed over to computers. The design results automatically generated by computer can be quickly displayed graphically, which is convenient for designers to judge and modify the design in time; Computers can be used to process graphic data related to editing, enlarging, reducing, translating and rotating graphics. Cad can reduce the labor of designers, shorten the design cycle and improve the design quality. Development Overview The first computer drawing system was born in the United States in 1950s, and passive computer-aided design technology with simple drawing output function began to appear. In the early 1960 s, cad surface patch technology appeared, and commercial computer drawing equipment was introduced. In 1970s, a complete cad system began to take shape. In the later period, raster scanning display which can produce realistic graphics appeared, and various forms of graphic input devices such as manual cursor and tablet were introduced, which promoted the development of cad technology. In 1980s, with the appearance of powerful microprocessors and storage devices made of VLSI, engineering workstations came out, and cad technology was gradually popularized in small and medium-sized enterprises. Since the mid-1980s, cad technology has developed towards standardization, integration and intelligence. Some standard graphical interface software and graphical functions have been introduced one after another, which has played an important role in promoting the popularization of cad technology, software transplantation and data enjoyment. The structure of the system has changed from a single function to a comprehensive function, and a computer integrated manufacturing system integrating computer-aided design and computer-aided manufacturing has emerged. The application of solidification technology, network technology, multiprocessor and parallel processing technology in cad greatly improves the performance of cad system. Artificial intelligence and expert system technology are introduced into cad, and intelligent cad technology appears, which greatly enhances the problem-solving ability of cad system and makes the design process more automatic. Now, cad has been widely used in electronic and electrical, scientific research, mechanical design, software development, robotics, clothing, publishing, factory automation, civil construction, geology, computer art and other fields. The composition of the system is usually based on an interactive computer system with graphic function. The main equipment includes: computer host, graphic display terminal, graphic input board, plotter, scanner, printer, tape drive and various software. Engineering workstation generally refers to a single-user interactive computer system with super minicomputer function and three-dimensional graphics processing ability. It has strong computing power, uses standard graphics software, has a high-resolution display terminal, and can work in a local area network with resources, forming the most popular cad system. Personal computer (pc) system is cheap, easy to operate and flexible to use. Since 1980s, the performance of pc has been continuously improved, and the software and hardware have developed rapidly. In addition, with the application of graphics cards and high-resolution graphic displays and the development of pc network technology, a large number of cad systems composed of PCs have appeared and are on the rise. Computer-designed secondary spherical graphics input and output devices are mainly composed of graphics input and output devices in computer-aided design, in addition to the host and general peripheral devices. Interactive graphics system is particularly important for cad. The general function of the graphic input device is to send the coordinates of each point on the plane to the computer. Common input devices include keyboard, light pen, touch screen, joystick, trackball, mouse, tablet and digitizer. Graphic output devices are divided into soft copy and hard copy. Soft copy devices refer to various graphic display devices, and human-computer interaction is essential; Hard copy devices are usually used as attachments for graphic display, which copy images to the screen for storage. There are three commonly used graphic displays: directional beam display, storage tube display and raster scanning display. Directional beam display is the earliest application. In order to make the image clear, the electron beam must constantly redraw the graphics, so it is also called refreshing display. Easy to erase and modify graphics, suitable for interactive graphics. The storage tube displays the saved images without refreshing, so it can display a large amount of data at a low price. The raster scanning system can provide color images, and the image information can be stored in the so-called frame buffer memory, so the image resolution is high. In addition to computer software, such as operating system and compiler, cad mainly uses three kinds of software: interactive graphic display software, cad application software and data management software. Interactive graphic display software is used for window opening, editing and viewing, graphic transformation and modification, and corresponding human-computer interaction. Cad application software provides geometric modeling, feature calculation, drawing and other functions to complete various special designs for various professional fields. The four elements of constructing application software are: algorithm, data structure, user interface and data management. Data management software is used to store, retrieve and process a large amount of data, including text and graphic information. Therefore, it is necessary to establish an engineering database system. Compared with the general database system, it has the following characteristics: the data types are more diverse, the entity relationship in the design process is complex, the values and data structures in the database often change, and the designer's operation is mainly a real-time interactive processing. The basic technology mainly includes interactive technology, graphic transformation technology, surface modeling and solid modeling technology. In computer aided design, interactive technology is essential. Interactive cad system means that when users design with computer system, people and machines can exchange information in time. With the interactive system, people can conceive, sample and modify at the same time, and the display results of each step can be seen from the screen of the graphic terminal at any time, which is very intuitive. The main function of graphic conversion is to connect the user coordinate system and the graphic output device coordinate system; Translation, rotation, scaling and perspective transformation of graphics; Graphic transformation is realized by matrix operation. Computer design automation Computer-built cad aims to realize the automation or semi-automation of computer-built design and development process. The research contents include functional design automation and assembly design automation, involving computer hardware description language, system-level simulation, automatic logic synthesis, logic simulation, microprogram automation, automatic logic division, automatic layout and wiring, and the corresponding interactive graphics system and engineering database system. Integrated circuit cad is sometimes included in the scope of computer design automation. . What is computer-aided design (CAD) Computer-aided design refers to the use of computers and their graphic devices to help designers with their design work. CAD for short. In engineering and product design, computers can help designers undertake tasks such as calculation, information storage and drawing. In design, computers are usually used to calculate, analyze and compare many different schemes to determine the best scheme; All kinds of design information, whether digital, literal or graphic, can be stored in the internal memory or external memory of the computer and can be quickly retrieved; Designers usually start with sketches, and the heavy work of turning sketches into working drawings can be handed over to computers. The design results automatically generated by computer can be quickly displayed graphically, which is convenient for designers to judge and modify the design in time; Computers can be used to process graphic data related to editing, enlarging, reducing, translating and rotating graphics. CAD can reduce the labor of designers, shorten the design cycle and improve the design quality. Overview of CAD development The first computer drawing system was born in the United States in 1950s, and passive computer-aided design technology with simple drawing output function began to appear. In the early 1960 s, cad surface patch technology appeared, and commercial computer drawing equipment was introduced. In 1970s, a complete cad system began to take shape. In the later period, raster scanning display which can produce realistic graphics appeared, and various forms of graphic input devices such as manual cursor and tablet were introduced, which promoted the development of cad technology. In 1980s, with the appearance of powerful microprocessors and storage devices made of VLSI, engineering workstations came out, and cad technology was gradually popularized in small and medium-sized enterprises. Since the mid-1980s, cad technology has developed towards standardization, integration and intelligence. Some standard graphical interface software and graphical functions have been introduced one after another, which has played an important role in promoting the popularization of cad technology, software transplantation and data enjoyment. The structure of the system has changed from a single function to a comprehensive function, and a computer integrated manufacturing system integrating computer-aided design and computer-aided manufacturing has emerged. The application of solidification technology, network technology, multiprocessor and parallel processing technology in cad greatly improves the performance of cad system. Artificial intelligence and expert system technology are introduced into cad, and intelligent cad technology appears, which greatly enhances the problem-solving ability of cad system and makes the design process more automatic. Now, cad has been widely used in electronic and electrical, scientific research, mechanical design, software development, robotics, clothing, publishing, factory automation, civil construction, geology, computer art and other fields. Functions of CAD system (1) Reuse of design components (2) Ease of design modification and versioning (3) Automatic generation of design standard components (4) Whether the design meets requirements and actual rules (confirm/verify the design according to specifications and design rules) (5) Simulated design without building physical prototype (6) Automatic design of components (a bunch of parts or other components). For example, manufacturing drawings and bill of materials (8) Direct output from design to production equipment (9) Direct output of machines for rapid prototyping or rapid manufacturing. At present, the main popular CAD softwares are: Zhongwang CAD (www.zwcad.com), autocad, www.zwcad.com Chen Hao CAD(CAXA), etc ... Among them, AutoCAD belongs to foreign products and is expensive. In order to solve the genuine problem, domestic manufacturers generally buy Zhongwang CAD, Chen Hao and other Zhongwang CAD, Chen Hao CAD and autocad, which are almost the same in operation. CAXA uses its own unique interface and operating habits.