Augmented Reality for the Manufacturing Industry: The Case of an Assembly Assistant Carola Botto * Politecnico di Torino Alberto Cannav ` o † Politecnico di Torino Daniele Cappuccio ‡ Politecnico di Torino Giada Morat § Politecnico di Torino Amir Nematollahi Sarvestani ¶ Politecnico di Torino Paolo Ricci || Politecnico di Torino Valentina Demarchi ** Politecnico di Milano Alessandra Saturnino †† Politecnico di Milano ABSTRACT This paper studies the impact of augmented reality (AR) on manual assembly operations in the manufacturing industry. A review of AR- based solutions in this field shows that assembly assistants capable to support the user in key activities (identification, handling, alignment, joining, adjustment and inspection) are particularly beneficial. Since assembly activities are generally not addressed within comprehen- sive solutions, an AR-based tool supporting all of them is proposed, and its effectiveness in terms of completion time and error rate is compared with the use of the corresponding paper-based instruc- tions. Results of a user study unveil that the proposed tool generally reduces the number of errors, but the time needed to complete the assembly tends to increase. Limitations of the current solution and potential directions for future work are discussed. Index Terms: Human computer interaction (HCI)—Interaction paradigms—Mixed / augmented reality; Applied computing— Computer-aided manufacturing 1 I NTRODUCTION The widespread availability Augmented Reality (AR) technologies is attracting the interest of both practitioners and researchers in a growing number of fields, including education [14], computer ani- mation [4], cultural heritage [7] and entertainment [10], to name a few. A very promising domain is represented by industrial applica- tions [12, 13, 16, 20]. A number of works in the literature already recognized the great potential of AR to support key industrial ac- tivities like, e.g., training [2], (collaborative) design [26], repair & maintenance [9, 11], customer service [8], as well as assembly operations [19], to name a few. With respect to the huge number of possible usage scenarios, this paper focuses on manufacturing, which promises to benefit more from the application of these technologies [3]. In particular, the work reported herein is aimed at investigating profitable applications of AR that could support the employees of a possible manufacturing company in performing their daily assembly tasks. Many studies on AR-based assistance for manual assembly have been conducted already, proving the effectiveness of this technology in enhancing the user experience while increasing the number of correctly assembled products and improving operation speed [28]. A lot of attention was focused, in particular, on the latter metrics as * e-mail: carola.botto@asp-poli.it † e-mail: alberto.cannavo@polito.it ‡ e-mail: daniele.cappuccio@asp-poli.it § e-mail: giada.morat@asp-poli.it ¶ e-mail: amir.nematollahi@asp-poli.it || e-mail: paolo.ricci@asp-poli.it ** e-mail: valentina.demarchi@asp-poli.it †† e-mail: alessandra.saturnino@asp-poli.it they represent the two Key Performance Indicators (KPIs) for the business of the considered companies [31]. In this paper, a specific use case represented by precision manu- facturing is addressed, although findings could be easily extended to other scenarios. Based on a review of relevant literature that is briefly summarized in Section 2, a list of features to be owned by a generic AR tool targeted to assembly operations were first identified. In this respect, it was found that integrating all of them in a single, comprehensive solution is not a common practice. Thus, an AR-based assembly assistant tool was developed trying to effectively integrate all the identified assembly operations, while coping with the needs of a manufacturing company operating in the field of precision positioning systems. The design steps are illustrated in Section 3.1, whereas a prototype implementation and the expected usage workflow are described in Section 3.2 and Section 3.3, respectively. The effectiveness of the devised tool has been investigated through a user study, which is presented in Section 4. Results obtained are discussed in Section 5. Finally, the limitations of the current design and implementation, as well as possible future works are reported in Section 6. 2 RELATED WORKS Works investigating the possibilities offered by the use of AR tech- nologies as well as studies of its impact in the manufacturing industry are not new. An early example is represented by the system proposed in [23] more than twenty-five years ago. In this work, a see-through head-mounted display (HMD) was used to superimpose a computer- generated diagram on a specific position in the real environment to support human operations in aircraft manufacturing. More recently, Nee at al. performed an extensive review of re- search activities carried out in the design and manufacturing domain considering AR applications [15]. In their work, they report in detail the current state of the hardware and software tools available for developing this kind of applications, by also discussing the associ- ated technological challenges. Moreover, they provide examples of AR-based collaborative design, robot path planning, and assembly applications, among others, offering hints on emerging trends in these fields. A similar work by Lamberti et al. addressed the fields of AR-based maintenance and repair [11], which share many aspects with assembly operations. As said, a review of relevant literature was performed in the present work with the aim to identify common aspects to be consid- ered, in particular, in the development of an AR-based tool support- ing the execution of assembly procedures. According to [17, 22, 30], the tasks characterizing assembly operations that could benefit more from the use of AR are the following: • identification and handling of the needed components (i.e., which ones are actually needed, and how have to be manipu- lated); • alignment of the components (i.e., which is the mutual position of two or more components, which are their contact surfaces, etc.);