动机可编程控制器(PLC)中英文翻译张.doc
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1、河南科技学院2009届本科毕业论文(设计)相关中英文资料资料题目:动机可编程控制器(PLC)学生姓名: 所在院系: 机电学院所学专业: 机电技术教育英文资料: Motivation Programmable Logic Controllers (PLC), a computing device invented by Richard E. Morley in 1968, have been widely used in industry including manufacturing systems, transportation systems, chemical process facil
2、ities, and many others. At that time, the PLC replaced the hardwired logic with soft-wired logic or so-called relay ladder logic (RLL), a programming language visually resembling the hardwired logic, and reduced thereby the configuration time from 6 months down to 6 days Moody and Morley, 1999. Alth
3、ough PC based control has started to come into place, PLC based control will remain the technique to which the majority of industrial applications will adhere due to its higher performance, lower price, and superior reliability in harsh environments. Moreover, according to a study on the PLC market
4、of Frost and Sullivan 1995, an increase of the annual sales volume to 15 million PLCs per year with the hardware value of more than 8 billion US dollars has been predicted, though the prices of computing hardware is steadily dropping. The inventor of the PLC, Richard E Morley, fairly considers the P
5、LC market as a 5-billion industry at the present time. Though PLCs are widely used in industrial practice, the programming of PLC based control systems is still very much relying on trial-and-error. Alike software engineering, PLC software design is facing the software dilemma or crisis in a similar
6、 way. Morley himself emphasized this aspect most forcefully by indicating Moody and Morley, 1999, P110: If houses were built like software projects, a single woodpecker could destroy civilization.” Particularly, practical problems in PLC programming are to eliminate software bugs and to reduce the m
7、aintenance costs of old ladder logic programs. Though the hardware costs of PLCs are dropping continuously, reducing the scan time of the ladder logic is still an issue in industry so that low-cost PLCs can be used. In general, the productivity in generating PLC is far behind compared to other domai
8、ns, for instance, VLSI design, where efficient computer aided design tools are in practice. Existent software engineering methodologies are not necessarily applicable to the PLC based software design because PLC-programming requires a simultaneous consideration of hardware and software. The software
9、 design becomes, thereby, more and more the major cost driver. In many industrial design projects, more than SO0/a of the manpower allocated for the control system design and installation is scheduled for testing and debugging PLC programs Rockwell, 1999. In addition, current PLC based control syste
10、ms are not properly designed to support the growing demand for flexibility and reconfigurability of manufacturing systems. A further problem, impelling the need for a systematic design methodology, is the increasing software complexity in large-scale projects. 1.2 Objective and Significance of the T
11、hesis The objective of this thesis is to develop a systematic software design methodology for PLC operated automation systems. The design methodology involves high-level description based on state transition models that treat automation control systems as discrete event systems, a stepwise design pr
12、ocess, and set of design rules providing guidance and measurements to achieve a successful design. The tangible outcome of this research is to find a way to reduce the uncertainty in managing the control software development process, that is, reducing programming and debugging time and their variati
13、on, increasing flexibility of the automation systems, and enabling software reusability through modularity. The goal is to overcome shortcomings of current programming strategies that are based on the experience of the individual software developer. A systematic approach to designing PLC software ca
14、n overcome 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 high-level
15、 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 s
16、afety rules. Thirdly, well-defined control systems design outcomes are conducive to automatic code generation- An ability to produce control software executable on commercial distinct logic controllers can reduce programming lead-time and labor cost. In particular, the thesis is relevant with respec
17、t to the following aspects. Customer-Driven Manufacturing In modern manufacturing, systems are characterized by product and process innovation, become customer-driven and thus have to respond quickly to changing system requirements. A major challenge is therefore to provide enabling technologies tha
18、t can economically reconfigure automation control systems in response to changing needs and new opportunities. Design and operational knowledge can be reused in real-time, therefore, giving a significant competitive edge in industrial practice. Higher Degree of Design Automation and Software Quality
19、 Studies have shown that programming methodologies in automation systems have not been able to match rapid increase in use of computing 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
20、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; IEC-61131-3, 1993; IEC 61499, 1998; ISO 15745-1, 1999 have been formed to fix and dissemi
21、nate state-of-the-art 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 components, and will provide methods to make large-scale
22、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
23、 as a performance destructor and complexity 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 o
24、ther hand. Secondly, software proliferates into complexity of unmanageable dimensions; software redesign and maintenance-essential in modern automation systems-becomes nearly impossible. Particularly, PLC programs have evolved from a couple lines of code 25 years ago to thousands of lines of code wi
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