Analyzing Safety of Collaborative Cyber-Physical Systems Considering Variability

Cyber-Physical System (CPS) is co-engineered interacting networks of physical and computational components that operate on different spatial and temporal scales. The safety goal of a single CPS is usually achieved by applying hazard analysis techniques and by following the standard processes defined in ISO 26262 and IEC 61508. However, the safety property may not be satisfied when multiple CPSs collaborate due to complexity, uncertainty, and variability. Therefore, a technique that would provide a hazardous-free collaboration for multiple CPSs is required to preserve sustainability. In this paper, we analyze the hazards arising due to variabilities in collaborative CPSs. We extend the hazard analysis techniques (FTA, FMEA, and ETA) to explore hazards with variability and developed a fault traceability graph from our extended techniques to trace the faults considered by multiple hazard analyses in collaborative CPSs with variability. To justify our proposed approach, a case study on the human rescue robot system was conducted to analyze hazards emerging as a result of variabilities. Finally, a tool (CPS Tracer) was developed to model the FTA, ETA, and FMEA with variability (v_FTA, v_FMEA, and v_ETA). It also and generates the fault traceability graph (v_FTG) that represents fault propagation route.