برنامه ریزی موازی با فعالیت های تعمیر و نگهداری Parallel machine scheduling with maintenance activities

1. Introduction and Problem Description The majority of machine scheduling models often assume that machines are available all the time for processing jobs over their associated planning horizon. However, this assumption is not realistic in many manufacturing situations, since machines require maintenance activity periodically to prevent malfunctions. During the associated maintenance activity machines are not available for processing jobs. Maintenance encompasses activities including installation, vehicles, equipment, or some physical assets enabling effective work. Preventive maintenance is an activity that a priori prevents potential faults resulting in malfunctions and also prevents critical nonavailability of the system. Note that maintenance costs cover a big percentage of the total operating costs, making it very reasonable to include maintenance activities in the production schedule (Ángel-Bello et al., 2011). In the airline industry, planned maintenance activities can reduce production time by as much as 15% (Laalaoui and M’Hallah, 2016). Moreover, especially in semiconductor manufacturing, it is often observed that machines are idle while waiting for maintenance personnel to do preventive maintenance, even though jobs are waiting. Thus, the operations managers have to create their production schedule carefully so as to minimize their costs while avoiding unexpected resource unavailability. Obviously, careful coordination between maintenance activity and job processing would result in a better schedule, which is the motivation for this study. Here, the authors consider a coordinated scheduling model that takes into account such associated machine maintenance activities.