# Enabling Technologies for Operator 4.0: A Survey
## 2 Framework of Operator 4.0 Solutions
### The Operator 4.0 Concept and Human-Cyber-Physical Systems
To support this goal, an overview concerning the elements of CPS from the perspective of operators is given in Table 3, and the levels of CPSs with a description of the functions and tasks are presented in Figure 2.  
As tasks should be transformed into a form that computers can understand, task analysis is becoming more and more crucial due to the difficulties of the externalization of the tacit knowledge of the operators [61]. Tacit knowledge contains all cognitive skills and technical know-how that are challenging to articulate [62; 63]. Without elicit tacit knowledge, the chance of losing critical information and best practice is very high [64]. Hierarchical task analysis extended with the'skill, rule and knowledge\" framework can capture tacit knowledge [65], an approach which has been proven to be useful in manufacturing [66]. Sensor technologies are essential to elicit tacit knowledge, for example the tacit knowledge of the operator can be captured by a'sensorized' hand-held belt grinder and a 3D scanner to generate a program of a robot that can replace the operator [67]. The modeling of the physical reality and realizing it in the CPS are critical tasks [68; 69; 70; 71]. These examples illustrate that Operator 4.0 solutions should be based on contextual task analysis, which requires precise chronological time-synchronization of the operator actions, sensory data and psycho-physiological signals to infer the cognitive states [72] and emotions [73] associated with the decisions and operator actions. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Design principle** & **Description** & **Application** \\ \hline \multirow{3}{*}{System integration} & It combines subsystems into one system. Vertical integration connects manufacturing systems and technologies [48]; horizontal integration connects functions and data across the value chain [49]. & Analytical operator \\ \hline \multirow{3}{*}{Modularity} & It is important for the ability of the manufacturing system to adapt to continuous changes [50; 51; 52]. & Augmented operator \\ \hline \multirow{3}{*}{Interoperability} & It allows human resources, smart products and smart factories to connect, communicate and operate together [50]. The standardization of data is a critical factor for interoperability because the components have to understand each other. & Collaborative operator \\ \hline Product personalization & The system has to be adapted to frequent product changes [53]. & \\ \hline \multirow{3}{*}{Decentralization} & It is based on the distributive approach, where the system consists of autonomous parts, which can act independently [50]. It simplifies the structure of the system, which simplifies the planning and coordination of processes and increases the reliability [54]. & Smarter operator \\ \hline \multirow{2}{*}{Corporate social responsibility} & It involves environmental and labor regulations. & Social operator \\ \hline \multirow{2}{*}{Virtualization} & It uses a digital twin, i.e., all data from the physical world are presented in a cyber-physical model [55]. & Virtual operator \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Design principles of Industry 4.0 applied to Operator 4.0 solutions. Sensors and feedback technologies of the interactive intelligent space can be used not only for improving the abilities of the operators, but also for the extraction of their tacit knowledge. In the following section, these technologies will be detailed.