Real‐time dynamic hoist scheduling for multistage material handling process under uncertainties

Abstract

in Wiley Online Library (wileyonlinelibrary.com).Multistage material handling processes are broadly used for manufacturing various products/jobs, where hoists are commonly used to transport inline products according to their processing recipes. When multiple types of jobs with different recipes are simultaneously and continuously handled in a production line, the hoist movement scheduling should be thoroughly investigated to ensure the operational feasibility of every job inline and in the meantime to maximize the productivity if possible. The hoist scheduling will be more complicated, if uncertainties of new coming jobs are considered, that is, the arrival time, type, recipe, and number of new jobs are totally unknown and unpredictable before they join the production line. To process the multiple jobs already inline and the newly added jobs, the hoist movements must be swiftly rescheduled and precisely implemented whenever new job(s) come. Because a reschedule has to be obtained online without violating processing time constraints for each job, the solution identification time for rescheduling must be taken into account by the new schedule itself. All these stringent requisites motivate the development of real-time dynamic hoist scheduling (RDHS) targeting online generation of reschedules for productivity maximization under uncertainties. Hitherto, no systematic and rigorous methodologies have been reported for this study. In this article, a novel RDHS methodology has been developed, which takes into account uncertainties of new coming jobs and targets real-time scheduling optimality and applicability. It generally includes a reinitialization algorithm to accomplish the seamless connection between the previous scheduling and rescheduling operations, and a mixed-integer linear programming model to obtain the optimal hoist reschedule. The RDHS methodology addresses all the major scheduling issues of multistage material handling processes, such as multiple recipes, multiple jobs, multicapacity processing units, diverse processing time requirements, and even optimal processing queue for new coming jobs. The efficacy of the developed methodology is demonstrated through various case studies.

Non-Cyclic Scheduling of a Wet Station

“…Some studies have considered a time window constraint including a no-wait time constraint in a cyclic schedule [20]- [29]. There have also been a few studies on real-time hoist scheduling [30], [31]. Lee et al [2] develop cyclic scheduling methods for a wet station.…”

Real‐time hoist scheduling for multistage material handling process under uncertainties

“…Zhao et al have recently developed an interesting mixed‐integer linear programming (MILP) model for real‐time hoist rescheduling in a multistage electroplating line. The system consists of a number of processing units and a single material handling hoist.…”

“…When one or multiple jobs arrive, an optimal hoist reschedule should be determined based on the current state of the jobs inline and the hoist. The objective is to minimize the time span required for processing all the jobs inline while satisfying the following three types of constraints: Hoist movement constraints. The release time for the hoist to drop any job in any unit and its corresponding lift time upon completion of processing are well defined so that the hoist is not required to handle more than one job at any time. Unit processing capacity constraints.…”

Branch-and-Bound Based Heuristic Scheduling for the Single-Hoist and Multiple-Products Production System

“…이 예제는 Zhao et al(2013)의 예 제를 기초로 하고 처리시간 및 호이스트 이동시간 등의 수치 들은 본 연구의 사례기업 상황을 반영하여 현실적으로 수정한 것이다. (7,6,4,3,1),   = (33, 3, 1, 4, 12), 처리순서는 (3, 1, 2, 4, 4, 2, 5, 3, 5, 3, 5, 5, 4, 3, 4, 5) ,197, 1,197, 1,196, 1,196, 1,196 …”