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Reactive schedule repair is a better alternative to total rescheduling of impaired job shop schedules. For ease of implementation in the job shops, heuristic-based schedule repair methods are preferred. However, the majority of the repair heuristics reported in the literature are capable of handling only a singular disruption to the schedule. On the contrary, real-world job shops are subjected to multiple complex disruptions that occur randomly over the span of the schedule. A new heuristic, modified affected operation rescheduling (mAOR), has been successfully used for repairing a majority of typical job shop disruptions such as absenteeism of workers, process time variations and arrival of unexpected jobs using a combination of generic repair steps. In the present work, the mAOR heuristic has been applied for repairing randomly occurring multiple disruptions under rigorous shop floor conditions. The relationship between the variation of shop floor conditions and the performance of the schedule repair heuristic is investigated to substantiate the effectiveness of the mAOR heuristic. The results of extensive experimentation indicate that the performance of the mAOR heuristic is superior to the right shift rescheduling heuristic (a commonly cited repair heuristic).

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Literature on job shop scheduling has primarily focused on the development of predictive schedules that generate an allocation sequence of jobs on machines. However, in practice, frequent deviations from a predictive schedule occur when the job shop experiences either external (e.g. unexpected arrival of urgent jobs) or internal disturbances (e.g. machine breakdowns) and renders the schedules inefficient. The reactive repair of the original schedule is a better alternative to total rescheduling, as the latter is not only time consuming but also leads to shop floor nervousness. Most of the existing schedule repair heuristics handle singular disruptions only. In this paper, the typical job shop disruptions are studied and their repair processes are decomposed into four generic repair steps, which are achieved using the proposed modified AOR (mAOR) heuristic. An extensive simulation study has also been conducted to evaluate the performance of the mAOR schedule repair heuristic, and the results indicate that the mAOR heuristic is effective in repairing job shop schedules when faced with disruptions.

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