Challenges in Future Mathematical Modelling of Hierarchical Functional Safety Control Structures within STAMP Safety Model

In the STAMP model, based on control theory, the control relationships between various system elements enforced by the closed Control Loops (CLs) are logical and functional. A literature survey emphasized the fact that for the moment STAMP and its main tools STPA and CAST are not associated with any numerical tools. The main rationale of our work is to understand whether STAMP matches to be a quantitative model. Furthermore, in a case that we find that numerical tools can be used in STAMP, we intend to bridge the gap between the logical-functional approach in STAMP and any of the suitable quantitative approaches applied in Engineering Control Theory (ECT). As a first step, a literature comparison was performed between the basic control parameters existing explicitly at the moment in the STAMP model, and those well known in the literature of ECT. The results reveal that there are many similar terms, especially related to conceptual and general definitions. However, we have observed that there are also basic quantitative parameters from ECT which are not yet referred to in STAMP as quantitative safety evaluation parameters. Another main finding is an inherent difference in various ECT related parameters and the CLs at the various hierarchical levels. ECT was originally developed to deal with physical systems. Thus, any machine related internal control loops within the lower-physical level of a Sociotechnical System (STS) can be directly addressed with quantitative methods from ECT. However, most of the human-machine interactions in the lower levels and the human and societal controls in the higher levels are at the moment not suitable for those methods. We assume these ECT parameters may have an important role in designing and examining systems safety and hence we suggest, should be integrated into STAMP model, in purpose to be able to enhance systems safety

Mode tracking and diagnosis of hybrid systems, an integrated approach

In this paper, we integrate information from a hybrid bond graph (HBG) model and discrete event systems (DES) into a fault diagnosis method for hybrid systems. In a pure HBG framework, mode change detection and isolation is handled by the mode change signature and the mode change signature matrix. In a DES approach, discrete states and faults are traced based on observable events and diagnosers. The integration of the two approaches is based on a new diagnoser that is driven by both, observable events and consistency indicators generated by continuous residuals. The proposed method allows not only to effectively trace the system mode, but also to decide whether this mode is faulty or normal. The new method is presented along with a theoretical example

Challenges in Future Mathematical Modelling of Hierarchical Functional Safety Control Structures within STAMP Safety Model

In the STAMP model, based on control theory, the control relationships between various system elements enforced by the closed Control Loops (CLs) are logical and functional. A literature survey emphasized the fact that for the moment STAMP and its main tools STPA and CAST are not associated with any numerical tools. The main rationale of our work is to understand whether STAMP matches to be a quantitative model. Furthermore, in a case that we find that numerical tools can be used in STAMP, we intend to bridge the gap between the logical-functional approach in STAMP and any of the suitable quantitative approaches applied in Engineering Control Theory (ECT). As a first step, a literature comparison was performed between the basic control parameters existing explicitly at the moment in the STAMP model, and those well known in the literature of ECT. The results reveal that there are many similar terms, especially related to conceptual and general definitions. However, we have observed that there are also basic quantitative parameters from ECT which are not yet referred to in STAMP as quantitative safety evaluation parameters. Another main finding is an inherent difference in various ECT related parameters and the CLs at the various hierarchical levels. ECT was originally developed to deal with physical systems. Thus, any machine related internal control loops within the lower-physical level of a Sociotechnical System (STS) can be directly addressed with quantitative methods from ECT. However, most of the human-machine interactions in the lower levels and the human and societal controls in the higher levels are at the moment not suitable for those methods. We assume these ECT parameters may have an important role in designing and examining systems safety and hence we suggest, should be integrated into STAMP model, in purpose to be able to enhance systems safety

Fault detection isolation and estimation in a vehicle steering system

Recently, a bond-graph-based fault detection and isolation (FDI) framework has been developed with a new concept of global analytical redundancy relations (GARRs) (Low, Wang, Arogeti, and Luo, 2009, 2010; Low, Wang, Arogeti, and Zhang, 2010). This new concept allows the fault diagnosis for hybrid systems which consist of both continuous dynamics and discrete modes. A failure of a safety critical system such as the steering system of an automated guided vehicle may cause severe damage. Such failure can be avoided by an early detection and estimation of faults. In this paper, the newly developed FDI method is studied in details using an electrohydraulic steering system of an electric vehicle. The steering system and faults are modeled as a hybrid dynamic system by the hybrid bond graph (HBG) modeling technique. GARRs are then derived systematically from the HBG model with a specific causality assignment. Fault detection, isolation, and estimation are applied, experimental setup is described, and results are discussed

Model-based Health Monitoring of Hybrid Systems

XII, 297 p. 246 illus.online resource

Mode Tracking of Hybrid Systems in FDI Framework

Abstract-A hybrid system combines continuous and discrete dynamics and runs with a set of modes. In [3],[4], we proposed an efficient health monitoring method for hybrid systems. This method utilizes unified constraint relations, named the Global Analytical Redundancy Relations (GARRs). Using GARRs for hybrid system health monitoring requires knowledge of the system's mode which is provided by a mode tracker. GARRs represent global information (i.e. information relevant to all modes), and the hybrid system properties can be analyzed across system's modes. In this paper, we utilize this unique feature to develop a GARRs based mode tracking approach. The most significant contribution of this development is the Mode-Change Signature Matrix, its derivation from the GARRs and its use for mode tracking