Integration of operational lockout/tagout in a joint production and maintenance policy of a smart production system

Abstract

Accidents during maintenance operations are frequently occurring and sometimes even fatal. The lack of energy locking is one of the main factors of accidents during maintenance. The Lockout/Tagout (LOTO) process aims to ensure the safety of workers by providing a control of equipment energies before and after preventive or corrective maintenance activities. However, LOTO is often seen as an unnecessary delay that increases production costs. The objective of this work is to minimize production and inventory costs of finished products, while guaranteeing the safety of workers during maintenance activities by the implementation of operational LOTO actions, which allows for production continuity during the securing of energy sources. This work studies the problem of production and maintenance planning of a smart production system that deteriorates according to its age affecting its reliability and availability. The system under study consists of a production unit processing a single type of parts and exposed to random failures and repairs. The decision variables for this control problem are the machine age dependent production and preventive maintenance rates of the machine. The proposed model is based on the stochastic optimal control theory and the optimality conditions are obtained by the dynamic programming approach. Such conditions are of the Hamilton-Jacobi-Bellman (HJB) type and have been solved by numerical methods for concrete industrial case applications. The developed model is validated using a numerical example and a sensitivity analysis is conducted to study the behavior of the system related to the variations of some parameters. A comparative study shows that the proposed operational LOTO strategy performs better than a traditional LOTO strategy in optimizing maintenance operations and reducing incurred costs. This study proposes new managerial policies in terms of joint management of production, maintenance and safety.