Scheduling of waiting queues in manufacturing workprocess using a human reliability measure

In the recent years the increasing recognition of the critical role of human factor in complex manufacturing systems, has focused a new attention towards the Human Reliability Analysis (HRA). During the phases of operations scheduling, engineers usually focus on problems caused by hardware, software or machinery breakdowns and they seldom pay attention to problems caused by the human error, which significantly may affect not only system reliability and safety but also the effectiveness of scheduling. The objective of the research is to look for a job sequence, in a waiting queue, able to improve the economic “expected profit”, considering the natural downsizing of the human performances during the workshift. Starting from a sequence of scheduled jobs, the model analyses the human error probability (HEP) for each manual operation, and assesses its error effects on the whole system. The model initially searches for the best job to be worked by the operator, according to his reliability and specific HEP value; moreover it automatically determines, for that operator, the optimal distribution of work pauses. The pauses are calculated in function of boundary causes that influence the human reliability and are focused on the reduction of HEP. The proposed methodology determine, if it exists, the optimal work sequence, that minimizes the HEP maximizing its deriving value of the global function of profit.