"ZuverSicht" – efficient enhancement of the reliability of safety-critical mechatronic systems

Status:

completed 09/2009

Aims:

The number of regulations governing machine safety is increasing, international product legislation is becoming stricter, and contractual penalties are on the rise. As a result, "high availability coupled with safety" is becoming an issue requiring action and research within the German machinery and installation construction sector. Conventional methods (such as the use of special components or solutions involving redundancy) result in increased costs, and place constraints on the flexibility of installations where adaptations are required. Conversely, cost-effective approaches which immediately place an installation in the safe state in the event of a fault prevent the installation as a whole from delivering its desired availability. The functionality and dynamics of modern machines and installations is increasing owing to the greater use of mechatronics. The focus of the project therefore lay upon mechatronic systems: these are systems in which mechanical, electronic and computing elements operate together. It is becoming evident that this complexity will be difficult to manage in the future by means of the existing proven methods.
The purpose of the "ZuverSicht" project was to enhance the reliability of machines and installations efficiently, whilst at the same time demonstrably meeting the safety requirements. A new, methodical modelling approach was planned, based upon a new architecture for mechatronic systems.

Activities/Methods:

Within the project, a new methodical approach, based upon a new architecture, was created for the development of systems and subsystems. A guide (also available in the form of a digital tool) was created by which the results of the project can be distributed more effectively following its completion. A tool was also developed for analysis of the reliability and safety of individual components and of the system as a whole. It delivers clear information throughout the development process on the reliability and safety status (such as on the number of dangerous failures per year).
Swift certifiability is important for the market success of mechatronic products employed for safety tasks. The testing of innovative and technologically complex safety products, which must by necessity be performed during the development process itself, has already been taken into account in the architecture model. The model's layer architecture forms the underlying concept for the attainment of safety. Parallel to the architecture, a sequence of steps has been described which permits a complete and efficient demonstration of safety.

Results:

The following project results were attained: a concept and a method for the efficient, appropriate demonstration of safety and reliability; the creation of tools serving this demonstration; an installation for demonstration purposes; and a guide, including glossary, in digital form.
The "ZuverSicht" concept makes provision for the task of demonstrating safety to be divided between two parties: the safety expert and the manufacturer of the installation. For the purpose of efficient demonstration, control patterns which are paramaterizable but already precalculated can be used for the implementation of safety functions. The patterns are generated in advance by the safety expert, who for this purpose supplies mathematical models for the patterns which are relevant in field application. The mathematical models are based upon Markov models which are generated systematically. A formal algorithm was developed for the individual steps of generation. The algorithm serves as the basis for implementation of a calculation tool. The resulting method then enables the safety expert to generate complex models automatically. The installation manufacturer need then only select the appropriate pattern for his safety function and add the reliability parameters of the control components which are used, in order to obtain the required system parameters for reliability and safety.
An implemented model installation for manufacturing technologies demonstrates the variety of typical safety functions. Safety analyses of parts of the installations were performed by means of the analysis method developed in the project.
Besides the principles of the subject, the guide in digital form includes, in particular, a description of the modelling method and documentation of the tools that have been produced. The guide takes the form of a wiki (a digital lexicon) in order to enable all contributors to extend the available information rapidly and simply and to make it available online to a wide audience.

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