Oscar Ljungkrantz

Formal Modeling of Function Block Applications Running in IEC 61499 Execution Runtime

The execution model in a new standard for distributed control systems, IEC 61499, is analyzed. It is shown how the same standard compliant application running in two different standard compliant runtime environments may result in completely different behaviors. Thus, to achieve true portability of applications between multiple standard compliant runtime environments a more detailed execution model is necessary. In this paper a new runtime environment, Fuber, is presented along with a formal execution model. In this case the execution model is given as a set of interacting state machines which makes it straightforward to analyze the behavior of the application and runtime together using existing tools for formal verification.

A Framework for Component Based Distributed Control Software Development Using IEC 61499

A framework for component based distributed control software is proposed. The primary application for the framework is in distributed control systems. The framework proposes new software components, called automation components that can be hierarchically embedded to produce new components. Automation components are also combined to produce hierarchical component based applications. The framework is independent of the execution platform, however it is shown how an application that is developed using the framework can be executed using IEC 61499 platform. The validity of the framework is evaluated using an industrial example of a reconfigurable manufacturing cell.

Formal Specification and Verification of Industrial Control Logic Components

Component-based programming frameworks for industrial control logic development promise to shorten development and modification times, and to reduce programming errors. To get these benefits, it is, however, important that the components are specified and verified to work properly. This work introduces Reusable Automation Components (RACs), which contain not only the implementation details but also a formal specification defining the correct use and behaviour of the component. This formal specification uses temporal logic to describe time-related properties and has a special structure developed to meet industrial control needs. The RAC can be formally verified, to determine whether the implementation fulfils the specification or not. A RAC prototype development tool has been developed to demonstrate this capability. The main difference between the RAC and other frameworks for formal verification of control logic is the specification modeling. In RAC, not only the implementation but also the specification is based on the structure and languages of conventional control logic, aiming at being easy to comprehend for control logic engineers. Several industrial examples are discussed in this paper, showing the benefits and potential of the framework.

A formal specification language for PLC-based control logic

Formal verification, using model checking tools, is promising in developing (IEC 61131) industrial control logic. Formal verification requires a formal specification of the properties to be verified. Specifications in model checking tools are typically expressed using temporal logic. However, the standard temporal logic dialects are not well suited for control engineers who do rarely have a background within computer science. In this paper a new dialect of linear temporal logic, ST-LTL, is introduced that intends to be easier to use for control engineers than the existing dialects. The relation of ST-LTL compared to existing temporal logic dialects is analyzed.

Implementing a Control System Framework for Automatic Generation of Manufacturing Cell Controllers

Quickly adapting the manufacturing system to the production of new or modified products is critical for manufacturers in order to stay competitive. For flexible manufacturing systems this typically implies modifications of the control programs. In previous work a framework for automatic generation of cell controllers has been developed. In this paper an implementation of the framework is presented. Important properties of the presented implementation are: the information from earlier design phases is reused; automatic code generation for faster development and reduced implementation errors; the supervisory control theory is used to generate control functions that are correct by construction; object oriented principles are used in order to allow the reuse of existing library functions. The implementation is generic in the sense that it may generate control programs for a number of target platforms, but in this paper the focus is on generating a control program for the Java platform. An industrial example of a reconfigurable manufacturing cell has been used in the implementation process and shows that the framework is feasible for large manufacturing systems.

Practice of Industrial Control Logic Programming using Library Components

This chapter discusses Programmable Logic Controller (PLC) programming practice, particularly the use of library components, in the automotive industry. A study of program structure and use of library components at two European car manufacturers is presented. The main purpose of the study is to provide understanding of current PLC programming in industry.

Towards Industrial Formal Specification of Programmable Safety Systems

Formal methods for specification and verification are promising in developing programmable logic controller (PLC) programs in manufacturing industry. Particularly this holds for safety PLCs, used to protect humans and equipment from injuries and damages. An important challenge though, is the development of formal specifications, typically a tough task for control engineers. This brief proposes a systematic work procedure that can be used as a first step of developing formal specifications of safety PLC programs in industry. The work procedure intends to facilitate the development of relevant formal properties for safety PLC program components. The formal specifications can be used for automatic formal verification of the components, using model checking techniques. This brief shows how the work procedure has been applied to industrial safety components, resulting in relevant and nontrivial specifications.

A Study of Industrial Logic Control Programming using Library Components

In this paper a study of logic control programming practices and use of library components at two European car manufacturers, is presented. The research provides results important to consider for researchers and PLC vendors when developing frameworks for control program generation, to cope with new requirements of flexible manufacturing systems. The main observations are: the programs, written mainly in Ladder Diagrams and Sequential Function Charts, frequently reuse pre-developed function blocks; it is important that the control programs can be understood and used for trouble-shooting by the operators; and finally, the code handles, besides automatic control, also safety and supervision, human machine interface, product data, communication etc., the code for automatic control is a minor part of the total code.

Simulink to UPPAAL Statistical Model Checker: Analyzing Automotive Industrial Systems

The advanced technology used for developing modern automotive systems increases their complexity, making their correctness assurance very tedious. To enable analysis by simulation, but also enhance understanding and communication, engineers use MATLAB/Simulink modeling during system development. In this paper, we provide further analysis means to industrial Simulink models by proposing a pattern-based, execution-order preserving transformation of Simulink blocks into the input language of UPPAAL Statistical Model checker, that is, timed (or hybrid) automata with stochastic semantics. The approach leads to being able to analyze complex Simulink models of automotive systems, and we report our experience with two vehicular systems, the Brake-by-Wire and the Adjustable Speed Limiter.

Organisation and communication problems in automotive requirements engineering

Project success in the automotive industry is highly influenced by requirements engineering (RE), for which communication and organisation structure play a major role, much due to the scale and distribution of these projects. However, empirical research is scarce on these aspects of automotive RE and warrants closer examination. Therefore, the purpose of this paper is to identify problems or challenges in automotive RE with respect to communication and organisation structure. Using a multiple-case study approach, we collected data via 14 semi-structured interviews at one car manufacturer and one supplier. We tested our findings from the case study with a questionnaire distributed to practitioners in the automotive industry. Our results indicate that it is difficult but increasingly important to establish communication channels outside the fixed organisation structure and that responsibilities are often unclear. Product knowledge during early requirements elicitation and context knowledge later on is lacking. Furthermore, abstraction gaps between requirements on different abstraction levels leads to inconsistencies. For academia, we formulate a concrete agenda for future research. Practitioners can use the findings to broaden their understanding of how the problems manifest and to improve their organisations.