The Study Of Process Scheduling Method In CAPP Expert System

CAPP(Computer Aided Process Planning)is the technology which combines process planning with computer technique. It plays a very important role in the information construction of enterprises. With the increasingly sophisticated requirement on the process design system by the informational manufacturing, people are more and more devoted to the CAPP expert system. Making a deep study of the CAPP expert system has become one of the hot spots in the application research of the artificial intelligence. After several years of study, however,there exist still many problems in the CAPP expert system.The first is that the application scope of the CAPP expert system is still very narrow. The second is that the fuction of the CAPP expert system is too few.The third is that the ablitity of the CAPP expert system is very low. Besides, the automatic scheduling of the process and the working step ,which is the key problem in the CAPP expert system, has not been sovled thoroughly. Therefore, aiming at the automatic process scheduling, the paper puts forward a series of solution methods and implementing ways, and open a new direction for the study of the automatic process scheduling of the CAPP expert system at the same time.The main study achievements in the paper comprise the following aspects:First, the paper adopts a better way (using machining elements) to describe a part, so constructs the input of the CAPP expert system. It paves the way for the integration of CAD and CAPP. The paper points out which information is essential to the CAPP expert system when we describe a part. Then we can take into account the information in the integration of CAD and CAPP.Second, the description of the non-axisymmetrical solid has been a difficulty for a long time. The paper adopts a new method to describe the non-axisymmetrical solid by using six view planes and the normal direction of the machining element. It makes an attempt to overcome the difficulty.Third, the paper presents a secondary input method to describe a part. When we have choosen the machining elements which are mentioned in the above, we must fill out a form of the machining elements affiliation. Only in this way, can the system confirm the position relation between the the machining elements. Based on this point, the process scheduling can be realized. Fourth, the paper stores the process knowledge by using a database instead of files and makes use of every flexible means to express various kinds of the process knowledge. The knowledge expression includes the datasheet field expression, the datasheet record line expression and the program expression. It paves a new way for the process knowledge base design.Fifth, the paper adopts a reasonable way to realize the reasoning mechanism. The reasoning mechanism includes the forward reasoning based on the single machining element, the datasheet field sequence control based on the single machining element and the datasheet record line sequence control based on many machining elements. The paper improves the reasoning abilities of the CAPP expert system considerably and enhances its practicability.Sixth, the paper combines the knowledge base with the fact base. It uses the knowledge base to store the process knowledge and the fact base to store the part feature information and the intermediate results obtained from the reasoning. It overcomes the shortage of the single knowledge base and extends the functions of the knowledge base.Seventh, the paper develops a model system of the CAPP expert system by Visual Basic and establishs the rule sets of the process scheduling for various kinds of parts. The CAPP expert system attains the primary practical requirement.The purpose of the paper is to surmount some technical difficulties ,so as to contribute to the development of the CAPP expert system.