industry 4.0 Technology: general issues 8 History of engineering & technology 7 sustainability 6 Industry 4.0 5 digital twin 5 optimization 5 deep learning 4 simulation 4 Internet of Things (IoT) 3 additive manufacturing 3 machine learning 3 manufacturing systems 3 response surface methodology 3 smart manufacturing 3 sustainable development 3 3D printing 2 COVID-19 2 COVID-19 pandemic 2 EEG sensors 2 Operator 4.0 2 Research & information: general 2 accuracy 2 air quality 2 augmented reality 2 benchmarking 2 calibration 2 carbon emission 2 conceptual framework 2 corporate social responsibility 2