# Human-Robot Collaboration: An Augmented Reality Toolkit for Bi-Directional Interaction
## 7 Conclusions  
This work deals with the development of an AR platform aimed at allowing the bi-directional interaction between a human operator and a collaborative robot through a HoloLens 2 device, supplied by the Automation, Robotics and Applied Electromagnetism Laboratory (AREA) and the Mechanical Design and Advanced Engineering Methods  
Figure 17: SUS scores for kinesthetic and AR interfaces; error bars represent 95\(\%\) CIs. Figure 18: Main statistically significant results of the SUS survey; error bars represent 95\(\%\) CIs. (MEDEA) of University of Basilicata. The work builds on the application presented in [8], whose main features consisted of communicating the robot status via a visual feedback in the AR environment and the robot intent by showing the planned end-effector trajectory to the operator. The novel contributions allow for a human-to-robot communication to be established by implementing the visualization of the robot workspace and the possibility to manipulate the trajectory by moving some way-points in the AR environment. Moreover, a safety system checks over the trajectory feasibility by taking into account the workspace limits. According to the authors' best knowledge, an AR platform that implements exactly the same features is not available in the literature. To this aim, a detailed comparative analysis cannot be performed. However, we have conducted a qualitative comparison with similar methods (see Table 3) taking into account the most relevant functionalities. A usability test has been conducted through a wide experimental campaign involving 45 voluntary users with different expertise levels, in which the proposed application is compared to a classical kinesthetic teaching task. In this campaign, the NASA TLX survey has showed a lower physical workload for the AR platform despite of the mental one. In case of XR-skilled users, the cognitive workload exhibited similar values for both kinesthetic and AR interfaces. Moreover, the System Usability Scale Questionnaire showed that users prefer the AR interface with respect to the kinesthetic one. Moreover, the users felt safer using the AR platform by about 4.4%. Furthermore, it has been discovered that visualizing the trajectory in the AR environment as a series of way-points was a key element in increasing user confidence. Future works will be devoted to enhancing safety and users' confidence during HRI through the real-time construction of virtual barriers that demarcate the boundaries of human and robot workspaces: if the robot attempts to cross this barrier, its speed is expected to decrease. Further research efforts will be focused on supporting complex tasks as the cooperative human-robot object transportation, managing information about the exchanged forces between the robot and the object. Other studies will be needed to reduce the mental workload by mean of optimization the HMD field of view. Moreover, collision avoidance algorithms in the AR environment will be implemented. At the end of the process, a second usability assessment will be carried out to address potential hardware and software issues. Conceptualization, G.C., N.C., M.S., F.P., F.C. and R.M. ; Methodology, G.C., N.C., M.S., F.P., F.C. and R.M. ; Validation, G.C., N.C. and M.S. ; Writing--original draft, G.C., N.C. and M.S. ; Writing--review & editing, F.P., F.C. and R.M. ; Supervision, F.P., F.C. and R.M. ; Project administration, F.P. and R.M. ; Funding acquisition, F.P., F.C. and R.M. ; Experimental validation: G.C. and M.S. All authors have read and agreed to the published version of the manuscript. This research has been supported by the Italian Ministry of University and Research under the grant PRIN 2022 COM\({}^{3}\) (COoperative Mobile Manipulators for Manufacturing) n.2022 ZLYBF5. Not applicable. Informed Consent Statement:Informed consent was obtained from all participants involved in the experimental study.