[Show abstract][Hide abstract] ABSTRACT: In case of failures in a PLC controlled process the problem of diagnosis arises. Today this is often a manual task. Whenever the failure in the controlled system is not directly related to an actuator, its sources have to be tracked back through the PLC program to the corresponding sensors. This process can be very time consuming. The presented work aims at providing a means for determining this effort and to assist the diagnosis process. To do so, software quality measures are studied. The evaluation of these measures on a program shows the most complex parts and hence gives hints on possible improvements. During the calculation of the measures graphical representations of some dependency relations are derived. These can be used as an aid for the engineer in the actual diagnosis process. Two case studies illustrate the presented approach.
[Show abstract][Hide abstract] ABSTRACT: Programmable logic controllers (PLCs) are still the workhorse of industrial automation. The programming and adaptation of the software for PLCs - i.e. the implementation of the control algorithms - are expensive and cumbersome tasks. Today the re-implementation of an existing PLC program on a new platform, as it is supported by industrial tools on a low level, requires considerable manual re-working by a specialist. Known re-implementation processes do not allow a fully automatic transfer to a new platform. Furthermore they lack re-documentation of the code which makes it hard to understand and to follow the implemented algorithms. To avoid these problems, this paper proposes a re-implementation concept for existing PLC programs based on formal methods. An application of this concept to a lab system is presented to assess its applicability
[Show abstract][Hide abstract] ABSTRACT: Programmable Logic Controllers (PLCs) have been of great eminence in manufacturing systems and will probably remain predominant for some time to come. To allow reimplementation on a new hardware and visualization of existing code, a formalization approach for PLC programs is proposed. The method presented here is not restricted to binary operations in the PLC code but also considers digital operations. In order to achieve compact visualization and efficient re-implementation an abstraction of the low level Instruction List (IL) programs is developed. The formalization of the abstracted code results in a compact finite state machine representation. The method is implemented using JAVA and XML technologies. The IL is converted to XML, the XML document object model (DOM) is used for parsing and scalable vector graphics (SVG) is employed to graphically represent the resulting automata. The presented approach is illustrated using STEP 5 IL from Siemens. The method is however generic, other IL dialects could be parsed if the corresponding description files are built.
Decision and Control, 2005 and 2005 European Control Conference. CDC-ECC '05. 44th IEEE Conference on; 01/2006
[Show abstract][Hide abstract] ABSTRACT: The developer of logic control systems is faced with increasing complexity of the functions to be implemented and, at the same time, increasing demands on the reliability of the resulting software. To analyze the reliability of such complex systems formal methods can be applied. One area of the corresponding research is focused on the application of model checking techniques to Programmable Logic Controllers (PLCs). In this paper a new method to formalize PLC programs together with a model of the cyclic behavior of the PLC is presented. The control systems behavior is modeled, and then the program, written in Instruction List, is formalized and integrated into the model. The formalization in SMV language is suitable for verification using BDD and SAT techniques. Both techniques are compared using first results of a case study
[Show abstract][Hide abstract] ABSTRACT: The complexity of existing PLC programs precludes dealing with or modifying them. The interest in the formalization of PLC programs has increased in recent years to overcome this problem. Formal methods can provide for the development of PLC programs, since they serve as a medium to analyze and verify them due to increased awareness of safety and quality. This is done by performing what is known as verification and validation (V&V). Moreover formal methods support reuse of already implemented PLC programs to meet new production demands. This paper examines different possibilities to formalize PLC programs. It explains the pros and cons of these different alternatives. The paper outlines a formal description of timers and counters used in PLC programs according to the alternative that fulfills the criteria best.
Robotics, Automation and Mechatronics, 2004 IEEE Conference on; 01/2005
[Show abstract][Hide abstract] ABSTRACT: Today there is a standard for the implementation of programs on programmable logic controllers (PLCs). Furthermore there are methods for the formal development of these programs. The standard allows the interchange of algorithms (e.g. if a new hardware should be used) and the formal methods allow the rigid prove of functionality especially needed in safety critical applications (e.g. using model checking). However, there is a lot of existing PLC programs that have been implemented in proprietary languages before a standard existed and even today formal methods are scarcely used. This paper outlines an approach to formalize existing PLC programs implemented in the widely used STEP5 language. It consists of two steps: first the modular structure of the program is transferred to a UML model and in a second step the algorithms contained in the modules are converted to finite automata. This conversion uses an abstraction method to avoid large automata.
Information Reuse and Integration, 2004. IRI 2004. Proceedings of the 2004 IEEE International Conference on; 12/2004
[Show abstract][Hide abstract] ABSTRACT: The development of the Internet and its technologies has been enormous in recent years and it represents a challenge for the field of automation. The wide spread use of the Internet technologies have invoked the idea of developing a standard platform for the remote control (RC) and remote maintenance (RM) of technical processes with the aim of high interoperability and inter changeability. This work presents a concept of Internet based RC and RM system which relies on the automatic control markup language (AConML). It describes mainly the components of the RC and RM system. AConML is a specific markup language defined through XML that was designed individually to complete these tasks. The idea of AConML rises to depose the reign of vendor specific platforms and object models invented as a result of competitions among of the developers of these systems.
Systems, Man and Cybernetics, 2004 IEEE International Conference on; 11/2004
[Show abstract][Hide abstract] ABSTRACT: Due to the growing complexity of PLC programs there is an increasing interest in the application of formal methods in this area. Formal methods allow rigid proving of system properties in verification and validation. One way to apply formal methods is to utilize a formal design approach in PLC programming. However, for existing software that has to be optimized, changed, or ported to new systems there is the need for an approach that can start from a given PLC program. Therefore, formalization of PLC programs is a topic of current research. This paper outlines a re-engineering approach based on the formalization of PLC programs. The transformation into a vendor independent format and the visualization of the structure of PLC programs are identified as an important intermediate step in this process. It is shown how XML and corresponding technologies can be used for the formalization and visualization of an existing PLC program.
American Control Conference, 2004. Proceedings of the 2004; 01/2004
[Show abstract][Hide abstract] ABSTRACT: In recent years, the interest in the formal-ization of PLC programs increased. The paper pro-vides a classification scheme for the works done in this field. This scheme includes the sources used for formalization, the level of the formalization process (i.e. the complexity of structures that could be han-dled by the approach), the aim of the formalization (Re-Engineering or Verification) and the formal model used to represent the formalized PLC pro-gram. The scheme is applied to several examples.