State of the art and future directions of digital twin-enabled smart assembly automation in discrete manufacturing industries

Digital twin (DT) technology is increasingly recognised for its potential to transform the manufacturing industry, particularly in assembly automation. By offering real-time insights and optimisation capabilities, DTs enhance efficiency, reduce costs, and improve product quality. This paper critically reviews DT-enabled smart factories in assembly automation, aiming to evaluate the current state, identify common practices, and propose a taxonomy for standardisation. The taxonomy outlines key factors in DT-enabled systems, including data sources, visualisation, applications, functional outputs, digital coupling, and IoT protocols. These classifiers help navigate the complex frameworks of DTs, guiding the design and implementation of assembly automation systems. Through a comprehensive analysis of 60 key publications, the review categorises DT objectives, propositions, and implementation technologies, identifying common themes and addressing gaps in current research. The findings emphasise the importance of integrating DTs with existing systems, ensuring reliability and security in data-driven DTs, and pursuing sustainable solutions beyond energy-intensive industries. This review not only informs future research but also provides a framework to guide industry practices in the development of DT-enabled assembly automation systems.