# The Role of Maintenance Operator in Industrial Manufacturing Systems: Research Topics and Trends
## 1 Introduction  
Maintenance significantly affects most of the total cost of production, from about 15% to 40% [1], production efficiency, on-time deliveries, capacity and overall cost efficiency, and product quality. Indeed, maintenance can mitigate machine deterioration in manufacturing systems and consequently improve product quality and machine reliability [2]. Therefore, maintenance contributes to gain high business performance, guarantee system availability, reliability, safety, and sustainability [3, 4]. Moreover, the evolution of production processes in recent decades influenced the way maintenance was managed and new maintenance policies emerged to meet this undesirable behavior, requiring efforts from all stakeholders to guarantee the commitment [5]. Therefore, the increase in the complexity and automation of modern production systems sheds light on the relevance of reliable maintenance processes and the need for competent human resources. Human factors cannot be ignored because of the high percentage of human errors and their economic, social and safety consequences in different industrial contexts [6, 7]. For these reasons, proper management of maintenance operators is essential. Human issues in maintenance are studied in the literature from different perspectives and some literature reviews were published in this research field. Reference [8] provided a systematic literature review focused on human errors in industrial maintenance, including studies until 2016. The review focused on exploring types and typical human errors in maintenance, error contributing factors, maintenancepolicies, methodologies for human error analysis, maintenance error consequences, and industrial sectors. A classification framework was instead proposed by Reference [9] to organize publications from the period 2004-2015 into three main categories: workplace design/macro-ergonomics, human error/reliability calculation methods and human resource management. Finally, a literature review focused on physical and physiological aspects of human factors in aircraft maintenance engineering was performed in Reference [10]. All these recent reviews showed a strong and growing interest in the research field of human issues in industrial maintenance. Indeed, humans are fundamental actors in manufacturing systems and maintenance activities are becoming more and more crucial, with respect to the past, for sustainable industrial operations. Due to such reasons, the role of maintenance operators is essential for guaranteeing safe, high-quality, and environmentally friendly operations. The aforementioned studies were then focused on specific aspects, such as a particular industrial sector, or conventional aspects of human issues and factors in maintenance. However, the current industrial paradigm focusses on cyber-physical systems and the integration of different technologies in conventional manufacturing operations to support human performance. This, inevitably, is leading to reconsider the role of maintenance operators, creating new challenges for enterprises and several research opportunities. Besides, to the best of our knowledge, no study investigated the wide field of 'human issues in maintenance activities', providing a comprehensive and objective overview of the main topics in the subject, as well as the research challenges related to the role of maintenance operators in the factory of the future. Therefore, this study first investigates the current state of the art role of maintenance operators in manufacturing systems, providing an overview of the main studies. A Systematic Literature Review (SLR) was conducted to identify and select the papers on the role of maintenance operators in production systems. Then, a topic modelling algorithm, based on the Latent Dirichlet Allocation (LDA) statistical approach, was used for detecting, in an objective way, the main topics of the selected papers, in order to provide the research trends on the subject.