【正文】 to overe shortings of current programming strategies that are based on the experience of the individual software developer. 2 PLC 英文資料 A systematic approach to designing PLC software can overe deficiencies in the traditional way of programming manufacturing control systems, and can have wide ramifications in several industrial applications. Automation control systems are modeled by formal languages or, equivalently, by state machines. Formal representations provide a highlevel description of the behavior of the system to be controlled. State machines can be analytically evaluated as to whether or not they meet the desired goals. Secondly, a state machine description provides a structured representation to convey the logical requirements and constraints such as detailed safety rules. Thirdly, welldefined control systems design outes are conducive to automatic code generation An ability to produce control software executable on mercial distinct logic controllers can reduce programming leadtime and labor cost. In particular, the thesis is relevant with respect to the following aspects. CustomerDriven Manufacturing In modern manufacturing, systems are characterized by product and process innovation, bee customerdriven and thus have to respond quickly to changing system requirements. A major challenge is therefore to provide enabling technologies that can economically reconfigure automation control systems in response to changing needs and new opportunities. Design and operational knowledge can be reused in realtime, therefore, giving a significant petitive edge in industrial practice. Higher Degree of Design Automation and Software Quality Studies have shown that programming methodologies in automation systems have not been able to match rapid increase in use of puting resources. For instance, the programming of PLCs still relies on a conventional programming style with ladder logic diagrams. As a result, the delays and resources in programming are a major stumbling stone for the progress of manufacturing industry. Testing and debugging may consume over 50% of the manpower allocated for the PLC program design. Standards [IEC 60848, 1999。 IEC611313, 1993。 ISO 157451, 1999] have been formed to fix and disseminate stateoftheart design methods, but they normally cannot participate in advancing the knowledge of efficient program and system design. A systematic approach will increase the level of design automation through reusing existing software ponents, and will provide methods to make largescale system design manageable. Likewise, it will improve software quality and reliability and will be relevant to systems high security standards, especially those having hazardous impact on the environment such as airport control, and public railroads. System Complexity The software industry is regarded as a performance destructor and plexity generator. Steadily shrinking hardware prices spoils the need for software performance in terms of code optimization and efficiency. The result is that massive and less efficient software code on one hand outpaces the gains in hardware performance on the other hand. Secondly, software proliferates into plexity of unmanageable dimensions。s very difficult to write a trigonometric function using ladder logic. ” Languages gaining acceptance include Boolean, control system flowcharting, and such function chart languages as Graphtec and its variations. And these’ s increasing interest in languages like C and BASIC. PLCs in process control Thus far, PLCs have not been used extensively for continuous process control. Will this continue? ” The feeling that I’ ve gotten,” says Ken Jeante, manager, product planning, Series One and Series Six products, at GE Frame North America, is that PLCs will be used in the process industry but not necessarily for process control.” Several vendorsobviously betting that the opposite will happenhave introduced PLCs optimized for process applications. Rich Ryan ,manager, mercial marketing, AllenBradley Programmable Controls Div, cites PLCs’ increasing use in such industries as food, chemicals, and petroleum. Ryan feel there are two types of applications in which they’ re appropriate.” One, he says, is where the size of the process control system that39。ve heard a lot about MAP in the last few years, and a lot of panies have jumped on the band wagon. Many, however were disappointed when a fullydefined and pleted MAP specification didn’ t appear immediately. Says Larry Kumara:” Right now , MAP is still a moving target for the manufacturers specification that is not final. Presently, for example, people are introducing products to meet the MAP products will be obsolete when the new standard for MAP, introduced.” Because of this, many PLC vendors are holding off on full MAP implementations. Omron, for example , has an ongoing MAPpatibility program, but Frank Newborn, vice president of Omron’ s Industrial Division, reports that because of the lack of a firm definition, Omron39。t yet talk to MAP. Since it’ s unlikely that an individual PLC would talk to broadband MAP anyway, makers are concentrating n proprietary works. According to Sal Provanzano, users fear that if they do get on board and vendors withdraw from MAP, they ‘ ll pulse width modulation control system be the ones left holding a munications structure that’ s not supported. PLC Introduction Programmable controller is the first in the late 1960s in the United States, then called Plc programmable logic controller (Programmable Logic Controller) is used to replace relays. For the implementation of the logical judgment, timing, sequence number, and other control functions. The concept is presented Plc General Motors Corporation. Plc and the basic design is the puter functional improvements,