The introduction of maintenance into a schedule reduces the frequency of unpredicted breaks caused by a machine failure and enables higher productivity, as well as in-time production. The advantage of this method is in the introduction of maintenance work into a schedule, taking into consideration a predicted time of failure. The paper presents the hybrid multi-objective immune algorithm (H-MOIA) aided by heuristic: minimal impact of disrupted operation on the schedule (MIDOS) for predictive scheduling. In this paper, the term ’disruption’ represents a machine failure. Due to disruptions which may appear on the shop floor (a machine failure, job priority changes, material unavailability etc,), it is more realistic to build a predictive schedule (PS). For example, when a set of tasks are assigned using a specific number of machines, processing times of operations are constant, and there is no disruption during a scheduling horizon on a shop floor (Wosik and Skołud 2009). All input data are known in advance in deterministic scheduling problems. The term ’scheduling’ refers to the allocation of a set of jobs, materials, tools and workers to predefined number of machines in order to optimize one or more objective functions.
This paper presents the research results and computer simulations. The H-MOIA + MIROS is compared to: (1) an algorithm based on priority rules: the LFJ and LPT and (2) Shifted Gap-Reduction. The H-MOIA + MIDOS is compared to two algorithms, identified in reference publications: (1) an algorithm based on priority rules: the least flexible job first (LFJ) and the longest processing time (LPT) (2) an Average Slack Method. The second objective is to compare the H-MOIA with various methods for predictive and reactive scheduling. The first objective of the paper is to present a hybrid multi-objective immune algorithm (H-MOIA) aided by heuristics: a minimal impact of disrupted operation on the schedule (MIDOS) for predictive scheduling and a minimal impact of rescheduled operation on the schedule (MIROS) for reactive scheduling. Rescheduling of disrupted operations, with a minimal impact on the stability and robustness of a schedule, is the main idea of the reactive scheduling method proposed. The foregoing of this constitutes the main idea of the predictive scheduling method proposed in the paper. It also results in higher productivity and in-time production. The introduction of maintenance work into a schedule reduces the frequency of unpredicted breaks caused by machine failures. Information about a failure-free machine operation time obtained in advance allows the users to plan preventive maintenance in order to keep the machine in a good operational condition. The high productivity of a production process has a major impact on the reduction of the production cost and on a quick response to changing demands.
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