Preventive Maintenance Policy For Multi-Machine Manufacturing System Considering Buffer Constraints

Modern manufacturing companies are facing multiple challenges such as fierce market competition and diverse customer needs.Advanced technology and efficient production systems are important guarantees for the core competitiveness of companies.Therefore,the health maintenance management of manufacturing systems raises new research topics.This paper focus on the multi-machine production system with intermediate buffer under steady production mode and batch production mode.Considering the health degradation of machines,production demand and structure characteristic of buffer system,dynamic cyclic scheduling policy of maintenance is proposed for each machine in the system.The policy reduces the computational complexity of decision-making procedure while effectively ensuring economic benefits.This thesis focuses on the following parts:1.Considering the complex structure of the multi-machine system with buffer,the inconsistency of the production rate of each machine leads to real-time buffer level fluctuation.Taking material conservation as a breakthrough,the production model is established to describe the real-time buffer on arbitrary location at any time.Sufficient buffer is able to support production when down machines exist in the system.Therefore,based on the real-time buffer level,the maximum opportunity window that one machine can be shut down without interrupting production is derived,and as an input to subsequent maintenance scheduling.2.Under stable production mode,reducing interruption and ensuring production efficiency are important goals when scheduling maintenance.Downtime of one machine creates opportunity for other machines.By maximizing the total reduction of maintenance and production expenditure based on the real-time buffer levels,a dynamic decision-making policy offers optimized maintenance combination cycle by cycle.The policy solves the difficulties of complex structure and dynamic variables in buffer system,as well as provides real-time and economically viable maintenance scheduling.3.Under batch production mode,randomness of batches,real-time buffer levels and machines degradation are comprehensively studied.The setup time between successive batches creates maintenance opportunities.Meanwhile,buffer can reserve surplus capacity and provide opportunities for maintenance.By minimizing the total maintenance expenditure during each batch cycle,the maintenance for each machine is scheduled at appropriate opportunity.Therefore,the economic benefits of the production system can be ensured.The joint scheduling of dynamic maintenance and batch production explores the maintenance decision theory research under the new production mode.