外文翻译--关于PLC的控制应用

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1、PLC Control of the Application1 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 facilities, and many others. At that time, the PLC re

2、placed 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.Although PC based control has started to come into place, PLC based control

3、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 of Frost and Sullivan1995, an increase of the annual sales volume to 15

4、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 PLC market as a 5-billion industry at the present time. Particularly, prac

5、tical problems in PLC programming are to eliminate software bugs and to reduce the maintenance 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.I

6、n general, the productivity in generating PLC is far behind compared to other domains, 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-progr

7、amming requires a simultaneous consideration of hardware and software. The software 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

8、debugging PLC programs Rockwell, 1999.In addition, current PLC based control systems are not properly designed to support the growing demand for flexibility and reconfigure ability of manufacturing systems. A further problem, impelling the need for a systematic design methodology, is the increasing

9、software complexity in large-scale projects.1 Objective and Significance of the ThesisThe 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

10、treat automation control systems as discrete event systems, a stepwise design process, 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 develop

11、ment process, that is, reducing programming and debugging time and their variation, 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 i

12、ndividual software developer.A systematic approach to designing PLC software can 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 o

13、r, equivalently, by state machines. Formal representations provide a high-level 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 repre

14、sentation to convey the logical requirements and constraints such as detailed safety 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 programm

15、ing lead-time and labor cost. In particular, the thesis is relevant with respect to the following aspects.(1) Customer-Driven ManufacturingIn modern manufacturing, systems are characterized by product and process innovation, become customer-driven and thus have to respond quickly to changing system

16、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 real-time, therefore, giving a significant competitive edg

17、e in industrial practice.(2) Higher Degree of Design Automation and Software QualityStudies 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 p

18、rogramming 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; IEC-61

19、131-3, 1993; IEC 61499, 1998; ISO 15745-1, 1999 have been formed to fix and disseminate 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 r

20、eusing existing software components, and will provide methods to make large-scale 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

21、control, and public railroads.(3) System ComplexityThe software industry is regarded 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 eff

22、icient software code on one hand outpaces the gains in hardware performance on the other hand. Secondly, software proliferates into complexity of unmanageable dimensions; software redesign and maintenance-essential in modern automation systems-becomes nearly impossible. Particularly, PLC programs ha

23、ve evolved from a couple lines of code 25 years ago to thousands of lines of code with a similar number of I/O points. Increased safety, for instance new policies on fire protection, and the flexibility of modern automation systems add complexity to the program design process. Consequently, the life

24、-cycle cost of software is a permanently growing fraction of the total cost. 80-90% of these costs are going into software maintenance, debugging, adaptation and expansion to meet changing needs.(4) Design Theory DevelopmentToday, the primary focus of most design research is based on mechanical or e

25、lectrical products. One of the by-products of this proposed research is to enhance our fundamental understanding of design theory and methodology by extending it to the field of engineering systems design. A system design theory for large-scale and complex system is not yet fully developed. Particul

26、arly, the question of how to simplify a complicated or complex design task has not been tackled in a scientific way. Furthermore, building a bridge between design theory and the latest epistemological outcomes of formal representations in computer sciences and operations research, such as discrete e

27、vent system modeling, can advance future development in engineering design.(5) Application in Logical Hardware DesignFrom a logical perspective, PLC software design is similar to the hardware design of integrated circuits. Modern VLSI designs are extremely complex with several million parts and a pr

28、oduct development time of 3 years Whitney, 1996. The design process is normally separated into a component design and a system design stage. At component design stage, single functions are designed and verified. At system design stage, components are aggregated and the whole system behavior and func

29、tionality is tested through simulation. In general, a complete verification is impossible. Hence, a systematic approach as exemplified for the PLC program design may impact the logical hardware design.关于PLC的控制应用1 前言可编程序的逻辑控制器（PLC），是由Richard E. Morley 于1968年发明的，如今已经被广泛的应用于生产、运输、化学等工业中。当时的PLC以软式连线逻辑或所

30、谓的继电器梯形逻辑（RLL）代替HARDWIRED逻辑，程序的语言看起来像HARDWIRED逻辑，因此构造时间从6个月降到了6天。虽然现在的PC控制已经开始得到应用，但由于PLC的高性能高效率和低价位以及高可靠性，使它仍然广泛应用于大多数工业控制中。而且，根据在PLC市场或Richard E. Morley的一项研究1995，一个每年1500万件PLC硬件营业额超过80亿美元预言被证实。虽然计算机硬件的价格正稳定地下降，但PLC的发明者，Richard E. Morley，认为PLC市场是一个40亿的行业。 尤其，在PLC程序设计过程中的实际问题是消除软件错误并且降低旧的梯形逻辑程序的维修费。

31、虽然PLC的硬件成本正在连续下降，降低梯形逻辑的扫描时间仍然是工业应用中面临的一个问题，以便低成本的PLC能被使用。通常，在产生PLC过程中的生产力比其他领域低，例如，VLSI设计，有高效率的计算机辅助设计工具。现有的软件工程方法学对基于PLC的软件设计不一定适用，因为PLC语言需要同时考虑硬件和软件。所以现在的软件工程方法学对建立PLC的软件设计不是必然可用的。在许多工业设计应用中，超过50%的人力被预定为测试和检查PLC程序错误。 另外，当今的基于PLC的控制系统没有被正确的用于支持日益增多的对制造系统的灵活性和重新配置的需求。另外，一个更进一步的问题：推进系统的设计方法学的需要，是大规模

32、的逐渐增加的软件复杂性。2 目标和意义 这篇文章的目标是PLC发展为一种系统的软件设计方法学。设计方法学包括基于状态转移模型的高阶层的描述，如离散系统，一个梯形程序的自动化控制系统，而且提供指导达成一个成功的设计。这个课题的结果将寻找到在管理控制软件开发过程中的错误，也就是说，减少经过模组化程序和调试时间和他们的变化，增加自动化系统的灵活性和促成软件可复用性。目标是克服单个软件开发者的经验的现行程序规划策略的缺点。设计PLC软件的有效方法能克服在生产控制系统的程序设计传统的方式里的缺点，并且能够在工业生产中有广泛的应用。自动化控制系统被形式语言做模型，相等的状态机可能被分析是否达到被要求的目标

33、。第二状态机描述提供一个结构化表示法传达合乎逻辑的需求和约束，像是详细的安全定则。第三，明确的控制系统设计结果有助于自动的代码产生。生产可运行的逻辑控制器上的控制软件能降低软件程序设计研制时间和人工成本。（1）用户驱动的制造业 在现代生产过程中，系统以产品和生产流程革新为特点，因此必须对改变系统要求迅速反应。主要的挑战是提供技术以便在变更需要和新的机会之后节俭重新配置自动化控制系统。设计和操作的知识可能被使用，因此，在工业实践过程中给予了重要的竞争优势。（2）设计的自动化和软件的高质量研究已经显示，在自动化系统过程中的程序设计方法没能与计算机资源的迅速增加相配合。例如，PLC的程序设计仍然是用

34、梯形逻辑图解依赖一种常规程序风格。因此，延迟和资源是制造业发展的一块主要的绊路石。测试和出错超过PLC程序设计被分派的50%的人力。标准IEC60848，1999；IEC611313，1993；IEC61499，1998；ISO15745-1，1999已经成为固定并且广泛使用的最新型的设计方法，但是他们通常不能参加发展有效率的程序和系统的设计知识。系统的方法将通过使用现有的新软件增加设计自动化的水平，并且提供方法使大规模系统设计容易。而且，它将会改良软件质量和可靠度，特别是危险的环境，例如飞机场控制和铁路。（3）系统的复杂性软件产业被认为是一个绩效析构函数的产生器。硬件价格的下降损坏了软件性能

35、的需要和效率。结果是庞大的低效率软件代码在速度上超过了硬件的性能。第二，软件到了难以控制大小的复杂性；软件重新设计和维护在现代化的自动化系统中几乎变得不可能。特别地，PLC程序已经在25年以前从一个电耦程序编码行进展到有输入/输出点的一个相似的数以千计的编码行。例如在增加安全放火墙上，现代自动化系统的灵活性给予复杂性计划设计过程。从而，软件的生命周期费用是永久增长总费用的一小部分。这些费用的80%90%作为软件的维护，调整，适应和扩大满足不断变化的需求。（4）设计理论发展如今，大多数的设计研究的主要焦点以机械或电气产品为基础。被计划研究的副产品之一将提高我们对基本设计理论和方法学的理解，通过把

36、它扩大到工程系统设计的领域。大规模和复杂系统的设计理论还没被完全发展。尤其，怎样简化一项错综复杂或者复杂的设计工作的问题还没被以科学方式处理。而且，在设计理论和最新epistemological正式表现在计算机科学和运筹学的结果之间，例如模型化系统分离事件，将推动以后的工程设计。（5）在合乎逻辑的硬件设计过程中的应用从一个合乎逻辑的视角，PLC软件设计类似于集成电路的硬件设计。现代VLSI设计对数百万部分和3年发展一个产品的时间感到极端复杂。设计过程通常被分成一个组成部分设计阶段和一个系统设计阶段。在组成部分设计阶段，单个的功能被设计并且证实。在系统设计阶段，零部件和整个系统性能和功能被模拟测试。通常，一次完整的验证是不可能的。因此，一个有效的适合PLC设计的程序可能挤入合乎逻辑的硬件设计中。