# Review of Responsiveness and Sustainable Concepts in Cellular Manufacturing Systems
## 1 Introduction  
The digitalization of manufacturing systems due to industry 4.0, the internet of things (IoT), big data, and cloud computing, has provided information that has enhanced the possibility of reacting to internal and external changes. Models and algorithms have become more important in using this opportunity to improve manufacturing efficiency, thus making production systems more competitive. The opportunity provided by digitalization has highlighted how the classical manufacturing systems, such as dedicated manufacturing systems (DMSs), flexible manufacturing systems (FMSs), and cellular manufacturing systems (CMSs), have some limitations in their ability to adjust to the latest industrial and market tendencies [1]. Group technology is a method to form a family of parts that have similarities in design and manufacturing. Cellular manufacturing systems (CMSs) are an application of group technology in which machines, equipment, and human resources are grouped together to form a cell that produce one or more family of parts. The manufacturing cell is organized to arrange equipment and machines to optimize the production process to follow the main benefits of the flow lines. Figure 1 shows the main characteristics of CMSs compared to dedicated and flexible systems. An example of flexible manufacturing systems are job-shops, which are production systems where machines of the same type are grouped into functional sections to manufacture a wider range of products. The dedicated systems, which work as flow-shops, are designed to produce a specific product. Machines and equipment are organized following the tasks' sequence of the product in a linear system that assures a direct flow with reduced movements. Figure 1 considers four main issues, which are flexibility, production efficiency, production volume, and production mix variations. CMSs are a trade-off between the two extreme characteristics of dedicated and flexible systems. As argued by [PERSON] et al. [2], companies, to meet global competitive challenges, have effectively used cellular manufacturing; indeed, some benefits of cellular manufacturing systems include increased throughput and reduced costs, also in terms of material handling. The authors state that reductions in cycle, downtime, setup, and material handling times can be achieved, as well as further improvements in process work, inventory level, factory layout size, and defect rates. Cellular manufacturing systems (CMSs) integrate the flexibility of the FMSs and the benefits of mass production systems, such as DMSs. CMSs consist of manufacturing cells designed to work on part families, thus improving productivity, reducing set-up times, and work in process [3; 4; 5]. In recent years, the reduction of energy consumption and greenhouse gas emissions has become a very important issue in manufacturing systems. One of the targets of the Europe Union for 2030 is to reduce energy consumption by 32.5% [6]. As reported in [7], more than 80% of emissions savings could be achieved through energy efficiency and renewable energy sources, to limit the increase of the global average temperature. Furthermore, sustainability is included in the 17 goals for building a better world, as reported in the 2030 UN Agenda for Sustainable Development [8]. For these reasons, researchers are focused on implementing energy efficiency, and finding strategies and policies for saving energy in manufacturing systems. Production systems must be able to react to continuous changes that may arise from external sources (such as demand) or internal sources (machine degradation and human resource management). Recently, the ability to adapt to the supply of energy sources and to improve the efficiency of the use of energy resources has become increasingly important. The development of industry 4.0 and IoT encourages manufacturing systems to be more innovative and resilient, and to improve their responsiveness to dynamic changes.