Cost effectiveness of a man-machine system considering physical conditionsof an operator

This paper presents two man-machine reliability models. A system consists o f one machine unit, one operator, and one event detecting monitor. The mach ine unit has three states, normal, abnormal, and failed. The event detectin g monitor may fail in two ways. If a machine unit becomes abnormal, the eve nt detecting monitor sends a signal, and the operator takes necessary actio ns. If the operator fails in the action in the cause of human error: the ma chine unit goes down. The condition of the operator is classified into two types, good and bad. The time to repair, and the human error rate both depe nd on the condition of the operator. The MTTF is obtained by using a Markov model and numerical computation. Furthermore, the optimal operating period which minimizes the overall cost is decided by using computer methods. Som e numerical examples are shown.