毕业设计我帮你

可编程控制器技术
可编程逻辑控制器（PLC），是由理察德.莫雷在1968发明的一种计算装置，已被广泛应用于包括制造系统，运输系统，化工过程设备，以及其他许多工业控制。当时，PLC软连线逻辑或所谓的继电器梯形逻辑取代了硬连线逻辑（RLL），一种视觉上相似的硬件逻辑编程语言。
虽然基于PC的控制已经开始出现，基于PLC的控制在大多数的工业应用将被保持，由于其更高的性能，更低的价格，和在恶劣环境下的高可靠性的技术。此外，根据对弗罗斯特和沙利文[ 1995 ] PLC市场的研究，增加的年度销售额1500万的PLC每年超过80亿美元的硬件价值进行了预测，尽管硬件价格稳步下降。PLC的发明家，李察德.莫雷，相当确定目前PLC市场是50亿元的产业。
虽然PLC广泛应用于工业控制中，PLC控制系统的程序在很大程度上仍然是依靠试验和错误。软件过程也一样，PLC的软件设计面对类似的方式困境或危机。莫利自己强调这方面最有力的指示“如果房子建造的像软件项目，一个单一的啄木鸟可以摧毁文明”。特别是，实际问题是在PLC编程软件缺陷消除和减少维修费用的梯形逻辑程序。虽然PLC的硬件成本的不断下降，使低成本PLC可用的行业问题仍然是减少梯形逻辑扫描时间。一般来说，PLC的生产力的产生是落后于其他领域，例如，超大规模集成电路的设计，在实践中高效的计算机辅助设计工具。现有的软件工程的方法不一定适用于PLC的软件设计，PLC编程需要同时考虑硬件和软件。因此软件设计成为越来越多的主要成本驱动。 在许多的工业设计工程中，超过分配给控制系统的设计和安装的人工土壤/预定测试和PLC程序[罗克韦尔调试，1999 ]。此外，PLC控制系统不适合设计的灵活性和可重构的制造系统的需求越来越大。在大型项目中需要推动一个系统的设计软件越来越复杂是进一步的问题。
设计PLC软件可以克服在传统程序生产控制系统缺乏系统的方法，并且在一些工业应用中总有很大的不同。由地方机器业决定自动化控制系统模型的正式语言或价地。形式化描述对被控制的系统的行为提供了一个高层次的描述。状态机可以分析评估他们是否达到想要的目标。其次，一个状态机描述提供了一种结构化的表示将逻辑的要求和限制，如详细的安全规则。第三，好的控制系统设计是有利于代码自动生成的能力，不同的逻辑控制器对商业产生可执行的控制软件可减少编程时间和劳动成本。特别是，客户驱动的制造和高水平的自动化设计和软件质量。
在现代制造业中，系统的特点是产品创新和工艺创新，要成为客户驱动必须快速响应不断变化的系统要求。一个主要的挑战是提供可以在经济上重新自动化控制系统在应对不断变化的需求的技术和新的机会。因此设计和操作知识可重复使用的实时性在工业实践中提供了一个重要的竞争优势。研究表明，在自动化系统中的编程方法已不能配合使用计算资源的迅速增加。例如，PLC的编程仍然依赖于传统的编程风格与梯形逻辑图。因此，程序上的延迟和资源是制造业进步的一个主要的绊脚石。
一个系统化的方法，通过重用现有的软件组件，提高设计自动化水平，并提供可管理的大规模系统设计的方法。同样，这将提高软件的质量和可靠性，将系统的高安全标准的有关事项，尤其是对那些如机场控制环境的有害影响，公共铁路运输。
软件业作为一个性能析构函数和系统复杂性的产生。硬件价格不断缩小战利品的代码优化和效率方面需要软件性能。结果是，一方面大量的和低效率的程序代码，并没有获得高的硬件性能。 另一方面，软件变得不可收拾的尺寸的复杂性；软件设计和维护在现代自动化系统的基本关系几乎是不可能的。特别是，PLC程序已经从几行代码25年前与I/ O点数量成千上万行代码的演变。提高安全性，比如新的政策对消防，以及现代自动化系统的灵活性增加了程序设计过程的复杂性。因此，软件的使用周期成本是一个永久的增长部分的总成本。80-90%的这些费用将软件维护，调试，适应和扩展以满足不断变化的需求。
今天，大部分设计研究的主要焦点都集中在机械和电子产品。这一研究计划的副产品是为了提高我们的设计理论和方法的基本理解延伸到外地的工程系统的设计。针对大规模和复杂系统的系统设计理论并没有成熟。特别是，如何简化一个复杂的或复杂的设计任务还没有被科学的处理。此外，建筑设计理论和新的认识成果的正式代表计算机科学和运筹学之间的桥梁，如离散事件系统的建模，可以提高工程设计的未来发展。
从逻辑的角度来说，PLC的软件设计与集成电路的硬件设计。现代超大规模集成电路的设计非常复杂，几百万个惠特尼产品开发时间用了三年。设计过程一般都分为一个组件的设计和系统设计两个阶段。在构件设计阶段，单一功能是设计和验证。在系统设计阶段部分是通过模拟汇总和整个系统的性能和功能测试。在一般情况下，一个完整的验证是不可能的。因此，一个系统化的方法体现的PLC程序设计可能会影响逻辑硬件设计。虽然高级PLC编程语言已经有一段时间了，但最近才流行并迅速发展。西门子能源自动化副总裁和总经理雷蒙德维尔。公司可编程控制的划分指出：“可编程控制器被用于更复杂的操作，比其他语言梯形逻辑变得更加实用，高效，强大。例如，用梯形图逻辑写一个三角函数是很困难的。包括布尔，控制系统流程图，以及日图及其变化等功能图语言获得接受。这是越来越多的关注语言如C语言和BASIC语言。
到目前为止，PLC还没有被广泛用于连续过程控制。这钟情况会持续吗？Ken Jeannette觉得，可编程控制器将在过程工业中使用，但不一定是过程控制。Triconex的总裁Bill Barkovtz预言未来所有的控制器，未来过程控制系统的业务将迎来比他们以前更多的PLC技术和更多的PLC功能。
通信是一个整体自动化工厂至关重要的个人自动化单元。我们已经在过去的几年里，听说过规范。很多，但是遗憾的是，完全定义完成的地图规范并没有立即出现。 Larry Kumara说：“现在，拉里库马拉地图仍然是一个移动的目标企业的规范。例如目前，人们仍然以地图2.1标准介绍产品。尽管2.1标准的产品将被新标准的地图3.0is淘汰。正因为如此，许多PLC厂家都紧盯着它的实现。例如，欧姆龙有一个正在进行的地图兼容性程序，但弗兰克先生，欧姆龙工业部副主席，报告说，因为一个缺乏公司的定义，欧姆龙的PLC还谈不上规范。
可编程控制器是60年代末首先出现在美国，然后叫可编程逻辑控制器PLC（可编程逻辑控制器）是用来取代继电器的。实现逻辑判断，定时，序列号，以及其他控制功能。这美国通用汽车公司提出的PLC的概念。PLC的基本设计思想是把计算机功能完善，灵活，通用等优点和继电器控制系统的简单操作方便，价格便宜等优点结合，控制器的硬件是标准的、全面的。根据实际应用目标的软件来控制控制器的用户程序存储器的内容，使控制器和被控对象方便连接。在70年代中期，该PLC已被广泛用来作为中央处理单元，微处理器，进出口模块和外部电路使用，即使当PLC不再是唯一的逻辑（IC）判断功能，大规模集成电路依然具有数据处理，PID调节和数据通信功能。国际电工委员会（IEC）颁布的标准草案中对可编程控制器PLC作了如下的定义：可编程控制器是一种数字运算操作的电子系统，专为在工业环境下应用而设计。它采用了可编程序的存储器，用来在其内部存储执行逻辑运算，顺序控制，定时，计数和算术运算。如操作指令通过数字式和模拟式的输入和输出的对各种类型的机械或生产过程的控制。可编程控制器及其有关外围设备，很容易地联成一个整体的工业控制系统，扩展其功能设计。可编程控制器对用户来说，是一种非接触式的设备，改变程序即可改变生产工艺。可编程控制器已成为工厂自动化的强有力工具，被广泛流行的复制。可编程控制器是面向用户的专用工业控制计算机，具有许多明显的特点。
  第一，可靠性高，抗干扰能力；
  第二，编程直观，简单；
  第三，适应性好；
  第四功能的改进，强大的功能界面。
PLC的抗干扰是极其优秀的，我们根本不用去关心它的使用寿命和工作场合的恶劣，这些所有的问题已不再成为我们失败的主题，而留给我们的是关心如何来利用PLC的内部资源为我们加强设备的控制能力，使我们的设备更加的柔性。
PLC的最大特点在于：电气工程师已不再在电气的硬件上花费太多的心计，只要将按钮开关或感应器的输入点连接到PLC的输入点上就能解决问题，通过输出点连接接触器或继电器来控制大功率的启动设备，而小功率的输出设备直接连接就可以。
人们在生产实践中看到,自动化给人们带来了极大的便利和产品质量上的保证,同时也减轻了人员的劳动强度,减少了人员上的编制.在许多复杂的生产过程中实现难以实现的目标控制、整体优化、最佳决策等。熟练的操作工、技术人员或专家、管理者都能够容易判断和操作,并获得满意的效果.人工智能的研究目标正是利用计算机来实现、模拟这些智能行为,通过人脑与计算机协调工作,以人机结合的模式,为解决十分复杂的问题寻找最佳的途径
  我们在各种场合看到了继电器连接的控制，那已经是过去的时代，如今的继电器只能作为低端的基层控制模块或者简单的设备中使用到；而PLC的出现成为了划时代的主题，通过极其稳定的硬件穿插、灵活的软件控制，使得自动化走向了新的高潮。
更高层次的发展需要我们不断的努力来取得。PLC的出现已经足足影响了几代人，我们也从上一辈的经验中获取了更多的知识和教训，来不断的发展PLC技术，将它推向更高浪潮。
 
外文翻译
Programmable Logic Controllers
Programmable Logic Controllers (PLC), a computing device invented by Richard.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 replaced the hardwired logic with soft-wired logic or so-called relay ladder logic (RLL),a programming language visually resembling the hardwired logic.
Although 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 of Frost and Sullivan [1995], an increase of the annual sales volume to 15 million PLC 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.Morley, fairly considers the PLC market as a 5-billion industry at the present time.
Though PLC 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 way. Morley himself emphasized this aspect most forcefully by indicating“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 maintenance costs of old ladder logic programs. Though the hardware costs of PLC are dropping continuously, reducing the scan time of the ladder logic is still an issue in industry so that low-cost PLC can be used.In 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-programming 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 debugging PLC programs [Rockwell, 1999].In addition, current PLC based control systems are not properly designed to support the growing demand for flexibility and reconfigur ability of manufacturing systems.A further problem, impelling the need for a systematic design methodology, is the increasing software complexity in large-scale projects.
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, Customer-Driven Manufacturing and Higher Degree of Design Automation.
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.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 PLC 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.
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.
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, 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 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-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 .
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.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.
Higher level PLC programming languages have been around for some time, but lately their popularity has been mushrooming. As Raymond Lavelle, vice president and general manager, Siemens Energy and Automation. Inc, Programmable Controls Division, points out :”As programmable controls are being used for more and more sophisticated operations, languages other than ladder logic become more practical, efficient, and powerful.For example, it'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 its variations.And these’s increasing interest in languages like C and BASIC.
Thus far, PLC have not been used extensively for continuous process control. Will this continue?The feeling that I have gotten is that PLC will be used in the process industry but not necessarily for process control,says Ken Jeannette.Bill Barkovtz, president of Triconex, predicts that all future controllers that come out in the process control system business will embrace a lot more PLC technology and a lot more PLC functionality than they ever did before.
Communications are vital to an individual automation cell and to the automated factory as a whole.We've heard a lot about MAP in the last few years. Many, however were disappointed when a fully-defined and completed 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 2.1standard.Yet 2.1-based products will be obsolete when the new standard for MAP,3.0is introduced.Because of this, many PLC vendors are holding off on full MAP implementations. president of Omron’s Industrial Division, reports that because of the lack of a firm definition, Omron's PLC don't yet talk to MAP.Omron, for example , has an ongoing MAP-compatibility program, but Frank Newborn, vice.
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 computer functional improvements, flexible, generic and other advantages and relay control system simple and easy to operate, such as the advantages of cheap prices combined controller hardware is standard and overall. According to the practical application of target software in order to control the content of the user procedures memory controller, the controller and connecting the accused convenient target.In the mid-1970s, the PLC has been widely used as a central processing unit microprocessor, import export module and the external circuits are used, large-scale integrated circuits even when the PLC is no longer the only logical (IC) judgment functions also have data processing, PID conditioning and data communications functions. International Electro technical Commission (IEC) standards promulgated programmable controller for programmable controller draft made the following definition : programmable controller is a digital electronic computers operating system, specifically for applications in the industrial design environment. It used programmable memory, used to implement logic in their internal storage operations, sequence control, timing, counting and arithmetic operations, such as operating instructions, and through digital and analog input and output, the control of various types of machinery or production processes.Programmable controller and related peripherals, and industrial control systems easily linked to form a whole, to expand its functional design. Programmable controller for the user, is a non-contact equipment, the procedures can be changed to change production processes.The programmable controller has become a powerful tool for factory automation, widely popular replication.
Programmable controller is user-oriented industries dedicated control computer, with many distinctive features.
First, high reliability, anti-interference capability;
Second，programming visual, simple;
Third, adaptability good;
Fourth functional improvements, strong functional interface.
The PLC anti- interference is very and excellent, our root need not concern its service life and the work situation bad, these all problems have already no longer become the topic that we fail, but stay to our is a concern to come to internal resources of make use of the PLC to strengthen the control ability of the equipments for us, make our equipments more gentle.
The PLC biggest characteristics lie in: The electrical engineering teacher already no longer electric hardware up too many calculations of cost, as long as order the importation that the button switch or the importation of the sensors order to link the PLC up can solve problem, pass to output to order the conjunction contact machine or control the start equipments of the big power after the electric appliances, but the exportation equipments direct conjunction of the small power can.
The people see in produce practice, automate brought the tremendous convenience and the product quantities for people up of assurance, also eased the personnel's labor strength, reduce the establishment on the personnel. The target control of the hard realization in many complicated production lines, whole and excellent turn, the best decision etc., well-trained operation work, technical personnel or expert, governor but can judge and operate easily, can acquire the satisfied result. The research target of the artificial intelligence makes use of the calculator exactly to carry out, imitate these intelligences behavior, moderating the work through person's brain and calculators, with the mode that person's machine combine, for resolve the very complicated problem to look for the best path.
We come in sight of the control that links after the electric appliances in various situation, that is already the that time generation past, now of after use in the mold a perhaps simple equipments of grass-roots control that the electric appliances can do for the low level only; And the PLC emergence also became the epoch-making topic, adding the vivid software control through a very and stable hardware, making the automation head for the new high tide.
The development of the higher layer needs our continuous effort to obtain. The PLC emergence has already affected a few persons fully, we also obtained more knowledge and precepts from the top one experience of the generation, coming to the continuous development PLC technique, push it toward higher wave tide.