Reliability-Based Preventive Maintenance for a Humanoid Robot System Under Dependent Competing Failure Processes

Modeling system reliability under dependent competing failure processes remains challenging due to the complex interactions among failure modes. In such systems, soft failures arise from the combined effects of continuous degradation and additional damage induced by abrupt external shocks, while hard failures are triggered by sudden and catastrophic stresses from the same shock process. In this work, a general reliability model is developed by incorporating coupling factors, permitting a formulation that is independent of specific degradation or shock models and does not rely on predefined failure mode classifications. Then, a tailored solution algorithm is designed for the proposed reliability model by decoupling the originally coupled structure and incorporating auxiliary variables and additional constraints. Building on this framework, a preventive maintenance strategy is developed to minimize the average long-run cost rate under periodic inspection. Finally, the reliability model and maintenance approach are implemented on a humanoid robot system, demonstrating the feasibility and effectiveness of the proposed methodology.