On Preventive Maintenance Strategy For Multi-unit Systems Under Changing Production Plan

With the development of economic, market competition become more and more fiercely. In order to ensure its power of competition, the manufacturing company has to control every step of the production process. However, with the expansion of the manufacture system, the control is more and more difficult. Meanwhile, with the population of more variety and minor batch production style, the requirement for the company is more like changeable, resulting the frequent change of the production plan. Besides, the manufacture system state determines the carrying out of the production, but it is determined by the maintenance activities. So, it is a difficulty for the company, to make adjustment between production plans with maintenance activities, resulting in more attention on the system maintenance decision under production plan.And so, based on the former single unit maintenance theory, taking the regular production system as object of study, the maintenance strategy of multi-unit system under production plan is investigated in this paper. The main contention of this paper show as below:Firstly, after the analyzing of the complexity of maintenance modeling for the multi-unit system, the system maintenance strategy is divided as two level strategies, the unit level and the system level. Unit level is responsible for the cost and period optimization of single unit and providing input for the system level, while system level aim at the system cost optimization under production plan.Secondly, maintenance optimization model is set in the unit level. With the brief summarize of the single unit maintenance strategy and cost structure during maintenance activities, equal period model under perfect maintenance is proposed, which is also convinced by the numeric test.Thirdly, under the production plan, taking the optimal result from the unit level, single unit preventive maintenance model under adjusting cost is proposed. For the collision between production plans with maintenance plan, a adjusting strategy is formulated in this paper, which means when the collision happens, the maintenance plan will be adjusted for the carrying out of job, ensuring the job can be carried out successfully. To solve the frequent change of production plan leading by changeable requirement problem, the maintenance strategy time span is no longer the whole production plan, single job is concerned as the time span instead in this paper. So the maintenance activities are decided before the beginning of the next job, which can be a new job for a new order, or a planning job. Meanwhile, the combination cost is deeply investigated for the evaluation of the adjusting strategy. The single unit maintenance strategy model under adjusting cost is finally proposed and convince by the numeric test.Finally, multi-unit maintenance strategy is set in the system level with the adjusting cost, group cost theory and opportunistic maintenance. Different strategies are proposed according to the linking style among units, and the costs are also investigated. With the combination of adjust strategy and group cost, maintenance model is proposed for multi-unit system. Then, series connection, parallel connection and series-parallel connection model are convinced by numeric test.To summarize, the maintenance decision model for the multi-unit system proposed in this paper can effectively deal with the need of multi-unit system maintenance, which is useful for the maintenance activities of multi-unit system.