# The Role of Maintenance Operator in Industrial Manufacturing Systems: Research Topics and Trends
## 5 Discussions and Research Trends  
The literature on human resources management and performance in manufacturing systems is wide and varied, but was mainly focused on the operators involved in processes like assembly, machining, or control ([94]). On the contrary, the impact of the human factors and the role of maintainers were not considered to be of interest to researchers, if not in those high-risk sectors in which man has always played an essential role. Indeed, the maintenance studies were mainly addressed to the technological and reliability aspects, and only in the last decade, the role of the people involved in this process has proven to be fundamental for the correct execution of maintenance activities. This is evident from the results of our review, which highlighted how the interest in this topic has gradually increased since 2013. The literature reviewed showed that the traditional methodologies developed to evaluate and improve the reliability of the operators, the management and scheduling strategies of the work activities, as well as the approaches to evaluate the operators' skills and competences were also applied to the maintenance context, allowing to explore a different environment with respect to the one for which they had been developed, leading to the birth of specific methodologies and approaches for maintenance field. At the same time, the progress of technologies and the evolution of the smart factory paradigm has led to the introduction in the industrial contexts of various types of enabling technologies to support and help the maintenance operator in carrying out his/her working activities. The analysis of the papers' contents and the identified topics allowed us to identify three main research trends, reported, and described below:  
1. **TREND 1**: Human reliability in maintenance activities;
2. **TREND 2**: Maintenance management strategies;
3. **TREND 3**: Supporting technologies for maintenance tasks. **TREND 1** focused on several approaches that were developed and used in the literature, having as a common goal the improvement of the maintenance worker's reliability level, and more generally, of the complex systems within the operator works. Despite technological improvements in the manufacturing systems, the human element remains essential to the quality of the work performed [42]. Over the years, several human reliability assessment (HRA) methods and approaches have been proposed to carry out a structured analysis of human reliability and human error probabilities for different industrial activities, as well as for the maintenance process. There are different techniques available to obtain a quantitative measure of human error probability (HEP). Based on the advantages and disadvantages of each technique, the selection of the most suitable traditional HRA technique, under the specific maintenance scenarios, was applied by most of the papers. All the papers are mainly focused on applying of existing methodology HRA for maintenance activity, on the classification and evaluation of PSF in a specific maintenance process, on investigating the main causes of human error in maintenance while only one paper highlights the effect of human error on machine performance. While the trend reveals a decline in the human error and reliability analysis over the years, the topic is still discussed in some studies because it can be considered as the starting point for human maintenance performance evaluation on a manufacturing system. **TREND 2** focuses on various organizational and managerial aspects impact considerably on the maintenance operator's performance, such as scheduling activities or assigning the right person to the right task. Human resource management is an important industrial challenge that maintains the level of global performance of manufacturing systems. This problem affects all industrial activities in general and maintenance activities.