**6. Conclusions**

Due to the complexity of AGV systems, they cause many decision problems, which are difficult to solve. The paper has presented an example of the Flexible Manufacturing System solution with the AGV transport system and discusses some issues related to the design and simulation of such systems. The stage of initial system design optimization is very important, and computer simulation enables the relatively easy elaboration and testing of various variants of manufacturing and logistics systems. On the other hand, excessive simplifications may be applied at the modelling stage, which will make the simulation not reflect the production system properly. It should be noted that detailed modelling is very labour intensive and requires the involvement of experienced specialists. Therefore, choosing what parameters are used in the modelling process and which metric is used to evaluate the

model is very important. In order to make the simulation more accurate and to evaluate the system's productivity, the use of Overall Equipment Effectiveness (OEE) metrics was proposed.

The results obtained from the presented simulations show that the OEE metrics can be used for the modelling and productivity evaluation of manufacturing and logistics systems, with the generalization of Overall Factory Effectiveness (OFE) and Overall Transport Effectiveness (OTE). The use of OEE factors also allows to compare the results obtained from different manufacturing systems. In the real world, most of manufacturing companies have OEE scores closer to 60%, but there are many of them with OEE scores lower than 45%, and a small number of world-class companies that have the OEE value higher than 85% [50]. According to that, the results of simulation can be also used to analyse the costs involved in the implementation of a given project and at the stage of in-depth design of the production system.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2227-9717/8/12/1648/s1.

**Author Contributions:** Conceptualization, A.K. and G.G.; methodology, A.K.; validation, K.F., G.G.; investigation, K.F.; data curation, G.G.; writing—original draft preparation, A.K.; visualization, G.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
