外国文献翻译

USING OF EXTENSIBLE FRAMEWORK FOR

DISTRIBUTED CONTROL DESIGN

Jiri Koziorek

Abstract:

The contribution brings results of a general framework extension development

with final aim to obtain a CASE-like tool for distributed control systems design. The

tool should be suitable for the systems with programmable controllers and should be

based on the international standards IEC 61131 and IEC 61499. The general

framework was developed at Department of Measurement and Control, VSB-TU Ostrava. The described system allows covering of main steps of design process from

system analysis to implementation of control application.

Keywords:

Distributed control, Control system design, Programmable controllers, CASE,

Control system analysis.

1、INTRODUCTION

A lot of the methods that are used in hardware and software engineering have common some general features. They often use graphic representation of described system, graphic diagrams with individual nodes connected by oriented (or not oriented) edges. The edges represent relations between two nodes of the system. The diagrams represent general mathematical structures - graphs that can be investigate using some techniques of graph theory.

The graph theory uses particular methods to express the diagram/graph structure and solution of various tasks defined over graph. Because diagrams describing particular HW or SW aspects of a system have also particular semantic interpretation, the interpretation can be given also to the results acquired by the applied graph theoretical method.

When we have a general kernel that covers universal features of the graphs, the particular tools can be created by the specialization of common general kernel - general framework kernel.

This idea was fundamental for creating common development base that can be extendable by particular extensions. Such common base (framework) was developed at Department of

2000 - 2003(Cernohorsky and Hrudka, 2003). As the software environment for its realization was chosen system the Black Box Component Builder (BBCB). BBCB has character of a framework itself and its power consists in the ability to provide a basis for development of more specialised frameworks by s elf-extending.

In year 2003 was realized first extension of general framework kernel (Hrudka, 2004). The extension implement CODARTS notation to the framework. CODARTS (Concurrent Design Approach for Real- Time Systems) is based on DARTS (Design Approach for Real-Time Systems) method of software design, which uses RTSAD (Real-Time Structured Analysis and Design). A software system is decomposed by using data and control flow hierarchy. CODARTS uses this methodology and appends facilities for object approach during the system analysis and modelling phase. CODARTS also supports the development of distributed systems.

The second, currently realized extension is the methodology for design of distributed control system with programmable controllers. The extension conforms to international standards with scope to PLC systems and should cover system design from stage of system analysis to implementation of control application. In following text, more details will be described.

The methodology should have following basic characteristics:

-to cover all stages of distributed control applications design

-to be suitable for control applications based on programmable controllers

-the international standards IEC 61131 and 61499 are basis for used models

-the principle of methodology is based on structured analysis and design approach。

2、TYPES OF DESIGN METHODS

There is a lot of methods for analysis and design of the real-time systems. An aim of using the design method is finding an optimal hardware and software architecture of the system and eventually partial or full implementation of the application code. Generally, there are two main approaches to system design:

-Structured analysis and design - a substance of the method is the design of a model where are depicted individual processes and their interconnections by data and control flows. The model is then a basis for implementation of application software.

-Object-oriented design - defines a structure of objects that reflects characteristics and

performance of individual elements of a real system.

At the present, the graphic methods realized at computers are frequently used. Such tools are called as CASE tools (Computer Assisted Software Engineering). They provide a graphic interface for making system analysis and design.

The methods based on object-oriented design are recently very popular. The most famous representative is UML (Unified Modelling Language). The UML is complex design methodology characterized especially by consistence of views that make the design easier in all stages of the application life-cycle. The UML methodology is a basis of several CASE tools as for example Rational Rose of Rational Software Corporation or Rhapsody of I-Logix Company.

The UML methodology and CASE applications that use it are suitable for design of the software in object oriented programming languages (as C++, JAVA etc.). The result of design is generated base of software application code. In the area of industrial control systems, programming languages enabling object oriented approach can be found very rarely.

The most popular control device today is programmable controller (PLC) which is used in majority of applications. The basic source, that defines programming languages for PLCs, is the international standard IEC 61131-3. There is not any object-oriented programming language at this standard. The basic element of its languages is not the object but a function block. Some PLC producers enable to program their PLCs in C language (for example B&R) or in others higher programming languages - but usually without object-oriented programming (OOP) support.

So, it is not reason to suppose that using of CASE tools based on OOP will be possible for design of industrial control applications in near future.

For such group of systems, the structured design is advantageous. In the near past, many design methodologies for structured design were developed but only some of them were realized as CASE tools. As an example can be mentioned a methodology for real-time applications software architecture design - DARTS (Design Approach for Real-Time Systems). It covers all steps of developed software life-cycle and contains criterias for optimal decomposition during design of real-time systems architecture. Despite of existence potentially

suitable design methods for control applications with programmable controllers, their using in practice in engineering companies is minimal.

The question is - Why? The design methods should ease the system analysis and the control software design and should make application development faster and more transparent. So this fact should mean their frequent usage.

The main problem is apparently caused by problematic link between CASE tool and concrete programming language. Another important fact is that absolute majority of PLC producers don’t provide the engineering tools based on such design methods for their products. For example Siemens Company, important world producer of the PLCs, gives in its technical documentation (Siemens, 2004) some recommendations for approach to design of control applications (similar to structured design), but engineering tools for Siemens PLCs don’t reflect them sufficiently. Similar situation is in engineering tools of others companies. Using stand-alone CASE tool in this situation can also increase level of transparency, reduce number of faults in developed application but means likewise more time and additional activities needed for the design.

The solution of described situation is existence of such development tool that covers application development from system analysis to software implementation for concrete control system. The basis for this tool can be any of existing structured design method. But it must be extended with specific set of abstractions for particular control system. Such extension of the general design tool should be based on widely accepted international standards and should follow future progress of control systems.

There are two international standards that are commonly supported by PLC producers and that provide recommendations for programming languages, communications, a design of distributed applications and other basic problems:

IEC 61131 - ”Programmable controllers“-fundamental standard for programmable controllers, especially parts 3 (programming languages) a 5 (Communications).

IEC 61499 - ” Function blocks for industrial- process measurement and control systems“ - Standard describes programming of distributed applications and using function blocks as elementary components of distributed applications.

3、INTERNATIONAL STANDARDS

As mentioned above, there are two important international standards concerning programmable controllers at the present - IEC 61131 and IEC 61499. The first is basic standard for PLCs, widely supported by industrial producers. The recommendations of standard are commonly accepted and they are implemented to majority of programming tools for PLCs. Part 3 (and also part 5) is applied most often.

The second, in the other hand, is the new standard defining function blocks as the basic elements of distributed control applications. Its recommendations aren’t commonly implemented in engineering tools of main PLC producers today and the standard can be taken as a definition of future development.

IEC 61131 Stαndαrd - Progrαmmαble controllers

The standard was published during years 1992 and 1998. It contains eight parts that cover various problems of PLC systems. Following list present the parts of the standard (Lewis, 1998):

1- General information - Definition of basic terminology and conception.

2- Equipment requirements and test - Electronic and mechanical construction, verification tests

3- Programmable languages - Structure of PLC software, languages and program processing.

4- User guidelines - Guidance on selection,installation and maintenance of PLCs.

5- Messaging service specification - Software components for communication between devices based on MAP ( Manufacturing Messaging Services ).

6- Communication via fieldbuses - Software components for communication using IEC fieldbuses.

7- Fuzzy control programming - Software components including standard function blocks for using fuzzy logic in programmable controllers.

8- Guidelines for implementation of languages for programmable controllers - Application and implementation rules for IEC 61131-3 languages.

For the purpose of creation the framework extension, the most important part is part no.3, 5 eventually 6.

Pαrt no. 3. This part defines a set of programming languages (5 languages) for PLCs and describes

common rules for program structure, notation, data types etc (IEC 61131-3, 1996). Defined languages do not support object-oriented programming despite of fact that one of them is high level programming language (ST - Structured Text). Standard defines the function block as basic element of the application. At the Figure 1 is described IEC 61131-3 software model.

Fig. 1. IEC software model.

Pαrt no. 5. This part concerns purely communications. It deals with features that enable PLC connected to communication network to exchange information and to initialize various actions. Part no. 5 deals with all aspect of external communication of PLCs.

IEC 61499 Stαndαrd - Function blocks for industriαl process meαsurement αnd control systems

The standard evolves an important idea defined in IEC 61131-3; the idea that function blocks are basic elements of local control application in PLC. IEC 61499 tells that the functions blocks are also basic elements of distributed control applications. The standard describes how the function blocks should looks like how to use them in distributed applications how to

Pristupove cesty

Task Task Task Tas k

Globaln岳a primo reprezentovane prom岳

nne

Komunikacni funkce

definovane IEC 61131-5

establish connection between them etc (IEC 61499, 2002; Lewis, 2001).

At the end of year 2003, the standard had four parts and works on it still continue:

1- Architectures - defines scope of the standard,basic terminology and describes types of models that are useful for distributed control application design.

2- Software Tools Requirements - contains specification of resources and devices types.

3- Application Guidelines - brings examples for implementation of software tools for tasks defined in previous parts.

4- Rules for Compliance Profiles - defines rules for compatibility profiles.

4、DESCRIPTION OF IMPLEMENTED METHODOLOGY

During the design of a distributed control application, an engineer must perform two main stages:

-Stage of functional design - an engineer analyses a physical structure of a controlled system and describes demands of highest level. This can be realized by set of blocks that represent main software components. At this level of design, physical placing of software block is not mentioned.

-Distribution of function stage - in distribution system design is necessary the distribution of functionality to process resources. IEC 61499 provides concepts and models for realizing this stage. Result of this stage is a network of function blocks that are allocated to process resources.

In following text are described models that are parts of developed framework extension.

The implemented methodology covers all steps of distributed control system design by following models:

-Function model - the aim of the model is to understand the system that should be controlled, describe its structure, decompose it to sub- systems or processes that can be then represented by software components.

-System model - the system model describes physical structure of a distributed control system. It defines relations between communicating devices and applications, defines way of communication between devices and its characteristics, and describes

distribution of applications between individual devices interconnected by communication

network.

-Device model - the model depicts which resources and hardware components are available in device and which applications use them, defines hardware configuration of the device and describes connected I/O signals.

-Resource model - the resource model describes which applications (or application parts) are processed by the resource. In the case of an application distributed to several resources, the resource model defines the ways of their communications. The way of communication is dependent to used communication connection but in fact, possibilities described in IEC 61131-5 can be chosen.

-Application model - the application model describes structure of applications, interconnections between sub-applications, between function blocks. When the function blocks are defined as basic elements of control applications, then the realization of application model is practically equal to creation of application.

5、A PILOT ANALYSIS AND DESIGN

The following pilot analysis and design was realized to demonstrate the above mentioned methodology. It presents all described models.

A coke-oven plant was chosen as a technological system for which the distributed control system should be designed. The coke-oven plant is complex system with number of

sub-systems that interact more or less between each other. The dimension of this technological system and its segmentation to

sub-systems are the reasons, why the coke-oven plant is optimal for control by distributed control system. During realization of pilot application, practical experiences with such type of technological plant were used because the author took part in realization of centralized control system of the coke-oven plant in Ostrava, Czech Republic (Koziorek, 1999).

Function design

The goal of function design is a description of coke- oven plant structure and functions. The result of this stage is relatively complicated set of models -

graphs. Each graph describes the system from highest level, through description of concrete parts of the system, to functional description of particular subsystems at the lowest level.

The coke-oven plant was divided to four parts:

-Co ke battery - main part of the plant, contains following subsystems -cokery gas

distribution, mining gas distribution, raw cokery gas distribution) and exhaustion.

-Changing device - a part that contains only one,relatively independent sub-system.

-Mix station - a part containing three sub-systems - MxG ratio, MG pressure, calorific value.

-Others subsystems - additional subsystems, that supports systems operation - hydro-injection,water distribution, pumps.

6、CONCLUSIONS

The contribution brings results of general frameworks extension development. It describes the structured design methodology that covers all steps of design process. The contribution contains also the pilot application of concrete technological system analysis and design. The design using presented methodology is very fluent and transparent which has positive influence at quality of distributed control applications.

译文

可扩展框架在分布式控制设计中的应用

Jiri Koziorek

摘要：

分布式控制系统设计的贡献带来的结果，最终目的是获得一个类似的工具来分布式控制系统设计的总体框架扩展开发。该工具应适用于可编程控制器的系统，并应根据国际标准IEC 61131和IEC 61499。总体框架是在测量和控制部门的发展。所描述的系统允许覆盖设计过程的主要步骤，从系统分析到控制应用的实施。

关键词：

集散控制，控制系统设计，可编程控制器，案例，控制系统分析。

1、简介。

在硬件和软件工程中使用的许多方法都有一些共同的特点。他们经常使用所描述的系统的图形表示，图形与个别节点连接的面向（或不面向）的边缘。边缘表示系统的两个节点之间的关系。该图表示一般的数学结构-图形，可以使用一

些技术的图论研究。

图论使用特定的方法来表达图/图结构和解决方案的各种任务定义在图。由

于图描述特定的硬件或SW方面的系统也有特定的语义解释，解释也可以得到的结果所施加的图论理论方法。

这个想法是创建共同发展的基础，可以扩展的特殊扩展的基础。这样的共同基础（框架）是在测量和控制部门的发展，俄罗斯、捷克共和国年2000 - 2003。作为其实现的软件环境的选择系统的黑盒组件生成器（BBCB）。BBCB具有框架本身和它的力量在于发展更多的专业框架的自我扩展提供基础的能力。

在2003年实现了总体框架的内核的第一个扩展（HRUDKA，2004）。推广实施CODARTS符号的框架。CODARTS（并行设计的方法对真实时间系统）是基于

飞镖（实时系统设计方法）的软件设计方法，它采用RESAD（实时结构化分析与设计）。使用数据和控制流层次分解软件系统。使用这种方法并追加CODARTS

方法为对象的设施在系统分析和建模阶段。CODARTS还支持分布式系统的开发。

第二，目前实现的扩展是可编程控制器的分布式控制系统的设计方法。扩展符合PLC系统的国际标准，应包括从系统分析到控制应用实现的系统设计。在下面的文字，更多的细节将被描述。

方法论应具有以下基本特征：

-涵盖分布式控制应用程序设计的各个阶段

-适用于基于可编程控制器的控制应用

-国际标准IEC 61131和61499是使用型号的基础

-方法论的原理是基于结构化分析和设计方法。

2、设计方法的类型。

实时系统的分析和设计方法有很多种。使用设计方法的目的是找到一个最佳的硬件和软件体系结构，并最终部分或全部实施的应用程序代码。一般来说，系统设计主要有两种方法：

-结构化分析和设计-该方法的实质是设计一个模型，通过数据和控制流描述个体-过程及其相互关系。该模型是应用软件实现的基础。

-面向对象设计定义了反映真实系统各个元素特性和性能的对象结构。

目前，在计算机上实现的图形方法经常使用。这种工具被称为CASE工具（计算机辅助软件工程）。他们提供了一个图形界面进行系统分析和设计。

基于面向对象的设计方法最近非常流行。最著名的代表是UML（统一建模语言）。UML是复杂的设计方法的特点，特别是由一致的意见，使设计更容易在应用程序生命周期的各个阶段。UML的方法是根据几个案例工具如Rational Rose Rational软件公司或I-Logix Rhapsody公司。

UML方法和案例应用，适用于面向对象的编程语言的软件设计（如C++、java 等）。设计结果是软件应用代码生成的基础。在工业控制系统的领域，编程语言，面向对象的方法，可以发现很少。

当今最流行的控制设备是可编程控制器（PLC），它在大多数应用中使用。的基本来源，定义了PLCs的编程语言，是国际标准IEC 61131-3。有没有任何面向对象的编程语言在这个标准。其语言的基本元素不是对象，而是一个函数块。一些PLC生产商可以用C语言编程（例如B & R）或其他更高的编程语言，但通常没有面向对象编程（OOP）支持。

因此，没有理由认为基于面向对象的CASE工具的应用将有可能在不久的将来设计工业控制应用。

对于这样的组系统，结构化设计是有利的。在过去，许多结构化设计的设计方法进行了开发，但只有他们中的一些实现CASE工具。作为一个例子，可以提到一个方法的实时应用软件体系结构设计-飞镖（实时系统的设计方法）。它涵盖了软件生命周期的所有步骤，包括最优分解指标的实时系统的设计中。尽管存在潜在的合适的设计方法与可编程控制器的控制应用，他们在工程公司的实践中使用的是最小的。

所描述的情况的解决方案是这样的开发工具，涵盖了应用开发从系统分析到软件实现的具体控制系统的发展。这个工具的基础可以是任何现有的结构化设计方法。但它必须扩展特定的抽象的特定控制系统。这种扩展的一般设计工具应基于广泛接受的国际标准，并应遵循未来的进度控制系统。

有两个国际标准，通常由PLC生产商支持，并提供编程语言，通信，分布式应用程序设计和其他基本问题的建议：

IEC 61131“可编程控制器”-可编程控制器的基本标准，特别是第3部分（编程语言）A 5（通信）。

IEC 61499功能块用于工业过程测量和控制系统”的标准描述了编程的分布式应用程序和使用功能块为基本组件的分布式应用程序。

3、国际标准。

如上所述，有两个重要的国际标准有关可编程控制器在目前- IEC 61131和IEC 61499。首先是PLCs的基本标准，广泛支持的工业生产者。标准的建议是普遍接受的，他们实施的大多数编程工具的PLC。第3部分（也是第5部分）最常应用。第二，另一方面，是定义功能块作为分布式控制应用的基本元素的新标准。它的建议通常不在今天的主要PLC生产商的工程工具中实现，标准可以作为未来发展的定义。

该标准是在1992和1998年出版的。它包含八部分，涵盖了PLC系统的各种问题。下面列出了标准的部分（刘易斯，1998）：

1 -一般信息-定义的基本术语和概念。

2 -设备要求和测试-电子和机械结构，验证测试