Hybrid two stage flowshop scheduling with secondary resources based on time buckets

This work studies a two-stage hybrid flowshop problem with secondary resources (workers). The goal is to minimise the average tardiness. The workers are assigned to the workstations by time buckets (work shifts), and the assignment changes during the planning horizon. Two versions of the problem are studied: (i) the case where the average efficiency of the workers determines the time to process jobs; (ii) the case where the efficiency of the slowest worker assigned to a workstation determines the time to process jobs. The problem is NP hard and a set of heuristics are proposed to generate job sequences and worker assignments. Computational experiments are performed on randomly generated test problems. The experiments revealed that the proposed heuristics are able to find a large percentage of the optimal solutions for small sized instances, while on large sized instances the heuristic performance depended on experimental factors.