Product design and manufacturing technology in the

Abstract: This paper discusses the relationship between virtual manufacturing technology and virtual reality technology, the research status of virtual reality technology and the application of product design and manufacturing in virtual reality environment, and develops a set of parking garage parameter design system in virtual reality environment

0, introduction

virtual manufacturing technology uses computer technology to comprehensively model and simulate the production and manufacturing activities to be carried out, including product design, processing, assembly, logistics, resource planning and allocation, organization and management, etc. At the stage of product design, we can simulate the shape, working condition and manufacturing process of the product in real time, check the manufacturability and design rationality of the product, and predict its manufacturing cycle and use performance, so as to modify the design in time, organize production more effectively and flexibly, shorten the product development cycle, and obtain the best product quality and benefits

according to the function of virtual manufacturing technology, it can be divided into product oriented virtual manufacturing technology and production process organization management oriented virtual manufacturing technology. The former focuses on the modeling and Simulation of product design, manufacturing, use, inspection and evaluation, while the latter focuses on the modeling and Simulation of production process planning, organization and management, resource scheduling, logistics, information flow, etc

virtual reality technology is to use computer technology to establish a realistic virtual environment. In this environment, people's feelings of vision, hearing and touch are the same as in the real environment, that is, there is a "immersive" feeling. People can immerse in this environment and interact with the environment in real time. This is its so-called "immersion", "real-time" and "active interaction". In this environment, the products designed, manufactured and used are not physical objects. They do not consume actual materials, nor do they need machine tools and other equipment. They are just so-called "digital products" of images and sounds. Using this digital product, we can carry out product appearance review and modification, assembly simulation and interference inspection, mechanical motion simulation, part processing simulation, and even product performance simulation and evaluation, so that in the upstream design stage of the product life cycle, we can eliminate the design defects, evaluate the feasibility and rationality of processing, predict the cost and performance of the product, and propose modification measures and methods. Virtual reality technology provides the best environment for us to implement concurrent engineering and agile manufacturing, reduce errors and rework, shorten the development cycle and improve product quality. It can be seen that virtual reality technology is most closely related to product oriented virtual manufacturing technology

virtual reality technology was just put forward in the 1980s. With the rapid development of computer technology, it received great attention in the 1990s and developed rapidly. It soon entered the practical stage. Especially in military and entertainment, the first successful application is exciting. The current situation is that, on the one hand, the development of its software and hardware technology is changing with each passing day; On the other hand, the price of its software and hardware is surprisingly high, and the price decline is also amazing. Some technologies are still in the primary stage, which are not satisfactory, and the software functions can not meet the needs

on the basis of existing conditions and technologies, how to give full play to the role of virtual reality technology and make beneficial contributions to our manufacturing industry is our

1. Basic requirements of virtual reality technology

from the way human beings obtain information, vision is the most important, accounting for 70% of the amount of information obtained by people, followed by hearing, touch and taste. In order to achieve realistic effects and meet people's visual and auditory habits, the image and sound response of the virtual environment is three-dimensional; In order to achieve real-time performance, the image should have a frame rate of at least 60 120Hz, and should respond to people's manipulation signals at any time, with a delay of no more than 0.1 seconds. Therefore, virtual reality technology requires high computing speed and display. Most systems and high-quality systems are developed on workstations and equipped with advanced graphics acceleration cards. However, in the past two years, the performance of microcomputer has been greatly improved, and high-quality virtual reality technology has been realized on microcomputer. The cost reduction and popularization of microcomputer will greatly promote the application and development of this technology

people obtain the shape, spatial position and speed of external objects through vision, which should be obtained through people's static, dynamic and physiological three-dimensional depth clues. Static depth cues mainly include the position, occlusion relationship, size and clarity of objects in space, which have been taken into account in our projection relationship of 3D modeling. The motion and position changes caused by the movement of objects require the computer to calculate and process images in real time. Only when it exceeds the human visual retention time, generally not less than 30 frames/second, can a smooth and stable image be obtained without flickering. This is what our current general 3D animation requires and should achieve. However, such three-dimensional graphics and animations are displayed in two dimensions on the screen, just like when we look at objects with one eye, they lack the sense of depth and three-dimensional of objects. Practice shows that human binocular parallax plays a decisive role in the sense of depth of objects. To achieve the natural three-dimensional effect of objects, we must use "two eyes" to see objects

in the computer virtual environment, the images of human eyes must be calculated and processed separately, and accordingly, separate image display is required. At present, helmet mounted displays are commonly used, but the price of high-resolution helmet mounted displays is more than $50000. In the desktop virtual environment, it is to display double images or alternate binocular images on the ordinary display, and then separate the images seen by both eyes through light valve glasses. Therefore, when using binocular image alternate display, the frame rate of the display must be more than twice that of the ordinary display mode. Considering the delay of light valve glasses, the flicker phenomenon will not occur until the frame rate is not less than 80Hz

images with binocular separation require that the computer must calculate and process images of more than 80 frames/second in real time on the occasion of 81 military day. This real-time requirement is very high, so workstations are often used as hosts. In the game software on microcomputer, the previous method used very low resolution and two-dimensional image. With the improvement of microcomputer speed, three-dimensional images can be used at present, but the resolution is still very low. Using high-end graphics accelerator card can greatly speed up the calculation speed, which can reach 32bit color, 1600*1200 resolution, 4m triangles/s and 100m pixel/s texture, which has made the virtual reality technology on the microcomputer platform enter the practical stage

in terms of manufacturing technology, the requirements for sound are generally low. In virtual reality systems such as military real-time confrontation training, spatial stereo effect is necessary

in the desktop virtual environment, the manipulators of human-computer interaction are mainly ordinary mouse, 6-DOF mouse, data glove and joystick. Data server and large projection screen are used in more perfect virtual reality system

the price of software and hardware of virtual reality system is relatively high. Therefore, different systems can be configured according to different purposes and needs, and the virtual environment with appropriate immersion depth will not make the system too complex and overburden the cost and maintenance. For example, the system used in automobile shape design focuses on displaying high-quality three-dimensional images, but the requirements of hearing and touch are very low. It can be manipulated with an ordinary mouse, and the real-time performance is also not high. For another example, in the part assembly simulation, in addition to the image, the maneuverability requirements are high, and 6-DOF mouse and data gloves can be equipped. In virtual reality systems such as vehicle and aircraft simulation training, wide vision, real-time control system and realistic sound effect are required. We should not only quickly respond to people's manipulation signals, but also realize the simulation of people's tactile feedback of force, displacement, etc

2. Application of virtual reality system

virtual reality system has been successfully applied in military, aerospace and other high-tech fields as well as entertainment and roaming. For example: cockpit system for astronaut and pilot training, battlefield real-time drill system (virtual battlefield), etc. Virtual reality system also has important applications in the process of product design and manufacturing, which can greatly improve the technical level of products, such as the design of Boeing 777 aircraft, Ford automobile shape design and collision experiment, roaming of factories and buildings, etc. At present, the best application effect is in the following aspects:

⑴ Product shape design:

for example, the shape design of automobile is a very important aspect of automobile. In the past, foamed plastic was often used to make shape models, which took time and labor through many evaluations and modifications. The shape design using virtual reality modeling can be modified and evaluated at any time. The modeling data after the scheme is determined can be directly used for stamping die design, simulation and processing, and even for advertising and publicity. It has great advantages in the shape design of other products (such as aircraft, construction and decoration, household appliances, cosmetics packaging, etc.)

⑵. Layout design of products:

in the layout design of complex products, virtual reality technology can be used to design intuitively to avoid possible interference and other unreasonable problems. For example, the machine layout, pipeline laying, logistics system, etc. in factory and workshop design all need the support of this technology. In the design of complex pipeline system and hydraulic manifold block, the designer can "enter" it to arrange the pipeline and check the possible interference and other errors. In the interior design of automobiles and airplanes, "intuition" is the most effective tool, and virtual reality technology can play an irreplaceable positive role

⑶. Motion simulation of mechanical products:

in the product design stage, we must solve the motion coordination relationship, motion range design, possible motion interference inspection and so on

⑷. Product assembly simulation:

there are thousands of parts in mechanical products that need to be assembled again. The coordination design and assembly ability are common mistakes of designers, which can often be found only when the product is finally assembled, resulting in the scrap of parts and the delay of construction period, and the failure to deliver in time, resulting in huge economic losses and reputation losses. Using virtual reality technology can be verified at the design stage to ensure the correctness of the design

⑸. Product processing simulation:

product processing is a complex process. The rationality of product design, machinability, selection of processing methods and machine tools, and possible processing defects in the processing process are sometimes not easy to find and determine in the design, and must be simulated and analyzed. For example, the shape of stamping parts or the design of stamping dies is unreasonable, which may cause the warpage and fracture of stamping parts, resulting in waste products. The shape of castings or the design of molds and gates are unreasonable, which is easy to produce casting defects and even scrap. The structural design of machined parts is unreasonable, which may lead to failure to process, or the processing accuracy cannot be guaranteed, or special processing must be adopted, which increases the processing cost and processing cycle. Through simulation, problems can be found in advance, and design modification or other measures can be taken to ensure the construction period and product quality

⑹. Virtual prototype and product performance evaluation:

Figure 1 reverse