## 2 Materials and Methods
### Virtual Data Production Model in the Digital Twin Concept  
The company has to possess correct data about the development of the production. The manufacturing environment is often fragmented and heterogeneous working as groups of independent production islands. Although the production islands can work highly effectively, the whole manufacturing system can seem like an untuned orchestra. In this environment we use only the local optimisations; any global optimisation of the whole manufacturing system is missing. Modern companies have to ensure a transparent course of production and strict registration of all events inside of it. The life of each product in the production system has to be exactly recorded in such a way that we will be able to follow it, if necessary, also in the future. These functions are nowadays ensured by the modern systems of production management [37]. The digital company is built on the basis of the scheme in Figure 1 where people, manufacturing machines, equipment, products and logistic systems are able to communicate and collaborate with each other [38]. The reason for connecting the digital and virtual world of the enterprise is the utilisation of a huge amount of data for making faster and more appropriate decisions. The interconnection of the products, manufacturing devices and people increases the effectiveness of the manufacturing machines and equipment; it saves resources and reduces the costs. The virtual company (the production data model) contains a lot of data that can be analysed and in the case of its collection and updating in real-time used for prediction. This would create a dynamic picture of the real production [39]. Through connecting all these three parts--the real, virtual and digital ones into one environment the so-called factory digital twin develops. When we are developing reliable software systems for supporting the planning and control procedures in the industry, the most difficult and most important step is to create an effective method of modelling a digital and data copy of the manufacturing system. Based on several studies [39, 40] verified design methodologies of the manufacturing systems in the digital company environment consist of the following stages:  
1. The introductory stage--acquiring the basic knowledge about the manufacturing assortment for which the production layout is being designed. 2. The project structure--this stage describes two basic activities--the definition of the manufacturing product and the current state analysis. 3. The process planning--the main part is created by processing the knowledge about the manufacturing processes. 4. The resource structure--creating the flow diagram dealing with complex analysis and realisation of the structure of the manufacturing system resources. 5. The realisation of the manufacturing layout--creating a digital model on the basis of findings from the previous stages. In cooperation with the IE department, we were able to identify the basic working instructions affecting the nature of the manufacturing employees' operation. For us to be  
Figure 1: Factory digital twin. (source: Authors). able to set up their parametric digital model of utilisation regarding individual activities, our project team had to define the following analysis areas:  
* The technological procedures, job designs of the manufacturing plan, cycle times of the machines. * The trial procedures and lists of the measurement devices for production. * The setup plans and instruction relating to the life span of individual tools. * The working instructions and working procedures for the machine operators. * The competencies of the operators, the dot plan. * The matrix of the machine set up with requirements on time. * The autonomous maintenance plan at the workplaces. The basic problems connected with the input data for setting up a parametric model of the production employees' utilisation are as follows:  
* Inaccurate planning due to inexact or incomplete data.