# Smart Interactive Technologies in the Human-Centric Factory 5.0: A Survey
## 2 Smart Interactive Technologies in the Human-Centric Smart Factory
### Augmented and Mixed Reality
#### 2.4.1 The Smart Factory Context  
**Applications: assembly and maintenance. ** Augmented reality is applied to guide and help workers in processes such as the assembly and maintenance of complex objects and quality checking, thus decreasing users' cognitive load and improving efficiency [56; 57]. More specifically, workers can interact with three-dimensional projections of the objects they are going to assemble and have the possibility of making any necessary checks before starting to build objects in the physical world. **Applications: access to technical data. ** Another possibility regards the provisioning of technical data, such as manuals, component availability, and maintenance history [57]: augmented reality can improve efficiency in providing relevant information in time as well as geo-located at the appropriate place. In this respect, [PERSON]. [58] identified a series of principles to improve user experience:  
* Interoperability, i.e., the use of the same standards for texts and visual elements, so as to facilitate human-machine interaction through documentation;
* Virtualization, i.e., paper documents are virtually copied on the machine, which can thus monitor user actions;
* Decentralization, i.e., documents are divided into sections, so that the machine can show users only the part they need at a certain time;Real-time functionality, i.e., the system must be able to analyze the collected data in real time in order to detect any errors. Similarly, technical documentation must be updated in real time, if necessary;
* Service orientation, i.e., carrying out each procedure as if it were a service (e.g., remote maintenance operations);
* Modularity, i.e., the adoption of a modular structure which allows greater flexibility, for example, when new technical procedures must be included within the existing documentation. An example of real-time technical data delivery is given by [59], who developed an app aimed to provide the operators on the shop floor with technical manuals, operating diagrams, maintenance history, and components availability in the warehouse, connected to the smart manufacturing software. **Available devices and technologies. ** As far as specific devices and technologies are concerned, augmented reality smart glasses (ARSG) are widely used in the context of smart factories [60]. However, they are prone to give rise to privacy-related issues, in that the use of cameras and other sensors could affect users' behavior and decision making. According to [61], in fact, privacy concerns are one of the factors influencing consumers' decisions to adopt ARSGs. Regarding mixed reality, the first commercial solution was Microsoft HoloLens, developed due to a collaboration between NASA and Microsoft. Devised at first for gaming purposes, Microsoft HoloLens were then widely applied on the shop floors of smart factories. A real-world application scenario was provided by Fifthingenium ([[https://fifthingenium.com/](https://fifthingenium.com/)]([https://fifthingenium.com/](https://fifthingenium.com/)), accessed on 29 July 2022), a company specialized in hybrid reality solutions for the industry sector: the Holo Prototype Viewer allows workers to interact with 3D models in their physical environments, creating a mixed reality experience. 4.2 Challenges and Guidelines for Augmented and Mixed Reality Interfaces in the Industry 4.0 Context  
Our review shows that augmented and mixed reality applications can be helpful when it comes to dynamically providing information to operators on production lines, as well as interactive manuals to be used in the assembly and maintenance areas. However, in addition to privacy-related issues, implementation can be difficult:  
* The smooth motions of augmented contents can be hard to obtain with ordinary mobile devices or tablet gyroscopes. * Depending on the projection surface texture and location, limitations may arise which may hinder an accurate understanding of the surface itself.