Reliability analysis of freight elevator systems based on FFMEC, FTA and BN

Reliability design is critical to the safe operation of complex systems, and the large-tonnage freight elevator (LTFE) is a typical complex system. In order to improve the reliability of LTFE in the textile dyeing and printing industry, a comprehensive analysis method is proposed, which is based on Fuzzy Failure Mode, Effect and Criticality Analysis (FFMECA), Fault Tree Analysis (FTA) and Bayesian Networks (BN). First, FFMECA is analyzed by fuzzy analytic hierarchy Process (FAHP) and entropy-weight method. The fuzzy function was designed according to the characteristics of parameters Severity (S), Occurrence (O) and Detection (D), and the Fuzzy Risk Priority Number (FRPN) are calculated and ranked to identify high-risk failure modes. Next, the key causes of failure are identified by the analysis of FTA and BN. FTA model is constructed by the high-risk failure modes, then the FTA model is mapped into a BN model, and an inferential analysis is executed. Finally, a case study is conducted, and six high-risk failure modes are found, including gate structure fault, tractor failure, electromagnetic braking fault. Improvement measures were proposed and simulation verified that the system reliability is more than 94%, meeting the system design requirements.