The current and expected advance of various technologies related to the "smart factory" and their integration in assembly lines at the age of Industry 4.0, creates a unique synergetic environment in which these assembly lines will operate. The paper starts by explaining the synergy advantages expected in a workstation from fusing information coming from variety of sensors and cameras connected as part of IoT, and analysed by Artificial Intelligent (AI) system. Next, the paper discusses the advantages of self-awareness of machines and work pieces added to the IoT environment to allow self-adjustment, self-reconfiguration and self-healing of the assembly system. Finally, the advantages of utilizing all of the above in a digital twin of the assembly system would also be discussed.