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无锡科技职业学院毕业设计中英文翻译
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 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 or, 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 representation 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 programming lead-time and labor cost. In particular, the thesis is relevant with respect to the following aspect 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 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 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 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 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 disseminate state-of-the-art design methods, but they normally cannot participate in advancing
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无锡科技职业学院毕业设计中英文翻译
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 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 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 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 have evolved from a couple lines of code 25 years ago to thousands of lines of code with a similar number of 1/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-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 [Simmons et al., 1998]. Design Theory Development
Today, the primary focus of most design research is based on mechanical or electrical 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. Particularly, 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 event system modeling, can advance future development in engineering design.
Application in Logical Hardware Design
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无锡科技职业学院毕业设计中英文翻译
From 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 product 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 functionality 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.
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无锡科技职业学院毕业设计中英文翻译
可编程控制器
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—连线逻辑或所谓的继电器梯形逻辑（RLL）代替HARDWIRED逻辑，程序的语言看起来象HARDWIRED逻辑，因此构造时间从6个月降到了6天。[Moody and Mrorley,1999]
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80亿美圆预言被证实，虽然计算机硬件的价格正稳定的下降。PLC的发明者，Richard E.Morley，认为PLC市场是一个40亿的行业。
虽然PLC被广泛的应用于工业生产中，但是基于PLC控制系统的的程序设计仍然非常依赖反复试验。PLC软件设计和软件工程一样面临着软件危机。Morley较多的强调了这个反面。
“如果房子像软件项目一样建造，一只啄木鸟就能破坏整个文明”。
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。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，是大规模的逐渐增加的软件复杂性。
PLCS（可编程逻辑控制器）是用于各种自动控制系统和过程的可控网络集线器。他们包含多个输入输出，输入输出是用晶体管和其它电路，模拟开关和继电器来控制设备的。PLCS用软件接口，标准计算器接口，专门的语言和网络设备编程。
可编程逻辑控制器I/O通道规则包括所有的输入触点和输出触点，扩展能力和最大数量的通道。触点数量是输入点和输出点的总和。PLCS可以指定这些值的任何可能的组合。扩展单元可以被堆栈或互相连接来增加总的控制能力。最大数量的通道是在一个扩展系统中输入和输出通道的最大总数量。PLC系统规则包括扫描时间，指令数量，数据
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