# Enabling Technologies for Operator 4.0: A Survey
## 2 Framework of Operator 4.0 Solutions
### The Operator 4.0 Concept and Intelligent Space  
In the previous section, the key functions of Operator 4.0 solutions were shown to be related to the monitoring and support of operator activities. The most significant trend is related to the development of human-machine interfaces that embrace interaction in a set of novel ways [100]. As the operator performs tasks, real-time information is provided about the production system and real-time support is received from it. Interactive human-machine systems had already been introduced in the Hashimoto Laboratory at the of University of Tokyo [101] where an intelligent Space (iSpace) system has been designed for the virtual and physical support of people and mobile robots [102]. Intelligent interaction space supports the operators to complete their work with high efficiency, high success rate and low burden [103]. The iSpace framework is shown in Figure 3. \begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Level** & **Function** & **Example** \\ \hline \multirow{3}{*}{Configuration} & Self-optimize & \\ \cline{2-3}  & Self-adjust & Prediction and online feedback with regard to quality issues [74; 75] \\ \cline{2-3}  & Self-configure & \\ \hline \multirow{3}{*}{Cognition} & Collaborative diagnostic and decision-making & Virtual Reality (VR) [76; 77; 78] \\ \cline{2-3}  & Remote visualization for humans & Augmented Reality (AR) [79; 80; 81] \\ \hline \multirow{3}{*}{Cyber} & Digital twin & Decision-making based on a digital twin [82; 83; 84] \\ \cline{2-3}  & Model of operator & Worker-movement diagram [85; 86; 87; 88] \\ \cline{2-3}  & & Monte Carlo simulation of a stochastic process model [89; 90] \\ \hline \multirow{3}{*}{Conversion} & Smart analytics & \\ \cline{2-3}  & Degradation and performance prediction & Online performance monitoring based on sensor fusion [91; 92] \\ \hline \multirow{3}{*}{Connection} & Sensor network & Wearable tracker [93; 94] \\ \cline{2-3}  & Indoor positioning system [95; 96; 97; 98; 99] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Levels of cyber-physical systems from the perspective of operators. Figure 2: Architecture of cyber-physical systems. The events within iSpace are continuously monitored by Distributed Intelligent Network Devices (DINDs) consisting of various networked sensors, e.g., indoor positioning systems and cameras for localization. DINDs interpret events in the physical space and provide services (feedback) to operators using physical devices, e.g., microphones, displays, etc. According to the horizontal integration concept, the proposed iSpace is also connected to suppliers and customers. This concept highlights that iSpace should relay on the CloudThings architecture that integrates Internet of Things (IoT) and cloud computing [104], as cloud computing enables a convenient, on demand and scalable network access to a shared pool of configurable computing resources. Resources, users and tasks are the three core elements of intelligent interaction space (see Figure 4). The user-resource-task model supports the design of interaction among these components [103], the interactions of which should handle how resources trigger the tasks and how the tasks are assigned to the operators based on their availability, performance and competence. Intelligent space should respond to requests from people, so the activities of the operators must be identified by cameras, internal positioning systems or based on voice signals, and these multi-sensory data should be processed by artificial intelligence and machine learning solutions [102]. The acquired information is transmitted via a wireless network and processed by dedicated computers, so any  
Figure 4: The design of connections between resources, users and tasks is the key to the design of intelligent interaction space. Figure 3: Intelligent Space (iSpace)-based integrated sensor signals can be used to monitor the work of the operators, extract their tacit knowledge, synchronize activities and provide contextualized information.