# Linking Scheduling Criteria to Shop Floor Performance in Permutation Flowships
## 1 Introduction
* Finally, since it is customary that different, conflicting goals have to be balanced in the shop floor (such as balancing work in process, and throughput), it would be interesting to know the contribution of the different scheduling criteria to shop floor performance in order to properly balance them. Note that, in two cases, the linkages between scheduling criteria and shop floor performance measures can be theoretically established. More specifically, it can be formally proved that makespan minimisation implies maximising the throughput, and that completion time minimisation implies the minimising the average cycle time. However, for the rest of the cases such relationships cannot be theoretically proved, so they have to be tested via experimentation. To do so, in this paper we carry out an extensive computational study under a different variety of scheduling criteria, shop floor performance measures, and instance parameters. Since the mathematical expression of the scheduling criteria is layout-dependent, we have to focus on a particular production environment. More specifically, in this paper we assume a flow shop layout where individual jobs are not committed to a specific due date. The main reason for the choice is that flow line environments are probably the most common setting in repetitive manufacturing. Regarding not considering individual due dates for jobs, it should be mentioned that both scheduling criteria and shop floor performance measures differ greatly from due date related settings to non due date related ones, and therefore this aspect must be subject of a separate analysis. Finally, we also assume that all jobs to be scheduled are known in advance. The results of the experiments carried out in this paper show that  
1. There are several scheduling criteria (most notably the completion time variance and one definition of idle time) which are poorly related with any of the indicators considered for shop floor performance. 2. Makespan minimisation is heavily oriented towards increasing throughput, but it yields poor results in terms of average completion time and work-in-process. This confines its suitability to manufacturing scenarios with very high utilisation costs as compared to those associated with cycle time and inventory. 3. Minimisation of one definition of idle times results in sequences with only a marginal worsening in terms of throughput, but a substantial improvement in terms of cycle time and inventory. Therefore, this criterion emerges as an interesting one when the alignment with shop floor performance is sought. 4. Minimisation of completion times also provides quite balanced schedules in terms of shop floor performance measures; note that it does not lead to the minimisation of WIP, as recurrently stated in the literature. The rest of the paper is organised as follows: In the next section, the scheduling criteria and shop floor performance measures to be employed in the experimentation are discussed, as well as the theoretically provable linkages among them. The methodology adopted in the computational experience is presented in Section 3.2. The results are discussed in Section 4. Finally, Section 5 is devoted to outline the main conclusions and to highlight areas for future research.