###### Abstract  
Augmented Reality (AR) has gradually become a mainstream technology enabling Industry 4.0 and its maturity has also grown over time. AR has been applied to support different processes on the shop-floor level, such as assembly, maintenance, etc. As various processes in manufacturing require high quality and near-zero error rates to ensure the demands and safety of end-users, AR can also equip operators with immersive interfaces to enhance productivity, accuracy and autonomy in the quality sector. However, there is currently no systematic review paper about AR technology enhancing the quality sector. The purpose of this paper is to conduct a systematic literature review (SLR) to conclude about the emerging interest in using AR as an assisting technology for the quality sector in an industry 4.0 context. Five research questions (RQs), with a set of selection criteria, are predefined to support the objectives of this SLR. In addition, different research databases are used for the paper identification phase following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) methodology to find the answers for the predefined RQs. It is found that, in spite of staying behind the assembly and maintenance sector in terms of AR-based solutions, there is a tendency towards interest in developing and implementing AR-assisted quality applications. There are three main categories of current AR-based solutions for quality sector, which are AR-based apps as a virtual Lean tool, AR-assisted metrology and AR-based solutions for in-line quality control. In this SLR, an AR architecture layer framework has been improved to classify articles into different layers which are finally integrated into a systematic design and development methodology for the development of long-term AR-based solutions for the quality sector in the future. augmented reality; industry 4.0; quality 4.0; metrology; assembly +
Footnote †: journal: Applied Sciences  
a solution in general and for manufacturing specifically [5]. These principles are real-time data management, interoperability, virtualization, decentralization, agility, service orientation and integrated business processes. An important aspect of Industry 4.0 is the synthesis of the physical environment and the virtual elements [6], which can be achieved by the advantages of AR together with the Cyber-Physical System (CPS). In the last few years, Augmented Reality (AR) has been constantly adapted by key companies on industrial innovation, such as General Electrics, Airbus [7] and Boeing. It has been employed for productivity improvement, product and process quality advancement (reducing error rates) [8] or higher ergonomics in diverse manufacturing phases to boost the transformation of Industry 4.0. AR studies in the quality sector have emerged, and have shown potential results in enhancing human performance in technical quality control tasks, supporting the Total quality management (TQM) and automomizing operators' decision making. Despite the mentioned advantages, there are still limited examples of AR's concrete implementation in manufacturing, especially for the quality sector. For this reason, the main objective of this paper is to conduct a state-of-the-art review of AR systematically in terms of technology used, applications and limitations, focusing on the quality context. This is to prepare for the digital transformation of Industry 4.0, which also leads to the change in the quality sector, known as Quality 4.0, and the adaptation of AR for quality control. However, not only the studies focusing on quality context but also  
Figure 1: Industrial revolutions and their characteristics based on [1]. the other relevant studies in the manufacturing context are considered to build a long-term roadmap for AR-based applications supporting Quality 4.0. To achieve this, a Systematic Literature Review (SLR) was performed to assure the reproducibility and scalability of the study, together with the objectivity of the results [9].