## 2 State of the Art
### Industry 4.0 Solutions Network  
The following is a very brief approach to an Industry 4.0 solutions network (I4.0 SN), considering the existence of a set of sequential phases, which, following a theoretical and conceptual case study, was proposed in order to respond to a challenge in an industrial context and on the shop floor of a company that produces test equipment for the wiring industry (a type of company that fits into the industrial reality under study) [1]. To this end, to come up with a credible solution that could be implemented in a real-world context, a series of pieces of information inherent to the company that are highly relevant to the study were collected beforehand [1]:  
* The existence of a production process characterised by high setup times and a high number of activities that depend on a worker's decision-making;
* The presence of such a company in a highly sought-after market in terms of personalisation, where constant technological innovation and the search for competitive advantage become key issues to be developed;
* A scenario in which almost all products are associated with a specific order, and in which there is rarely a second order for a product with the same characteristics;
* The existence of production orders that do not exceed five units per product, and orders associated with a single unit are common; a scenario in which the raw material used for production goes through several machining phases, in which several different industrial machines are used; and, the verification that each product results from the assembly of multiple specific parts, which in turn must be inserted into a given defined project, at the level of its production, since each project has a unique set of parts. In this context, there was an effort by [1] to guarantee the solution's compatibility with a wide range of industrial realities, to create and structure a type of production system, with the integration of a set of I4.0 technologies flexible enough to meet the specific requirements of each client and achieve a reduction in various activity times at the level of the production process in various phases without compromising the flow of the respective production system to be considered (in an approach aimed at mass customisation). The I4.0 SN, therefore, consists of a set of six main stages (identified by numbers from 1 to 6 in Figure 1), with the possibility of integrating an additional stage of importance in certain cases (including a extra feature stage, numbered 5.1 in the figure), connected by the organisation's network, in an IoT-based approach [1], as can be seen in Figure 1.  
A worker's identification at the workstation (stage 1) is the initial step in the network system. To begin working at a certain workstation, an employee needs to have their own special RFID card. This allows each workstation to have a unique RFID reader that is linked to a unique ID. Following the card's reading, the company's database automatically saves details about the time and workstation that a particular employee claims to be using [1]. This approach can be very helpful in calculating the cost of a particular process phase, but it does not have a significant effect on the production process itself. Furthermore, by giving accurate information on the productivity of employees and workstations, these data may benefit the company's human resources and logistical departments [1]. For the project folder with integrated QR (quick response) code (stage 2) operation within the network system, all project-related data (such as drawings and built-in materials) that are kept in the company's database must be associated with a QR code ID [1]. These days, most shop floors save this kind of information in actual folders containing numerous worksheets. The current proposal eliminates the need for physical paper by reducing it to a single sheet containing the project's identification and delivery date, along with a printed QR code that allows access to all remaining digitally available information.