## 4 Discussion and Main Conclusions
Obviously, toward establishing a viable solution, each aspect of HRI design (e.g., human factors, interaction roles, user interface, automation level, and information sharing [10]) should be tackled separately, so as to identify and address possible issues. We tried to add human comfort, naturalness, and the sense of trust to the picture, which are considered very important in HRI and have received limited attention in agriculture so far. Comfort and trust can contribute, to a great extent, to the feeling of perceived safety, which is among the key issues that should be guaranteed in synergistic ecosystems [6; 75; 76]. In other words, users must perceive robots as safe to interact with. On the other hand, naturalness refers to the social navigation of the robot though adjusting its speed and distance from the workers. To conclude, the present study investigated the possibility of using nonverbal communication based on hand gesture detection in real conditions in agriculture. Obviously, this framework can also be implemented in other sectors depending on the specific application at hand. Possible future work includes the expansion of the present system to incorporate more hand gestures for the purpose of other practical applications. Toward that direction, recognition models that can identify a sequence of gestures could also be useful. In addition, it would be interesting to examine the potential of combing hand gesture recognition with human activity recognition [52; 53] in order to propose a more fluid HRI and test the framework in more complex applications. More experimental tests should be carried out in different agricultural environments to identify possible motion problems of the UGV, which may lead to the application of cellular neural networks [77] to address them, similar to previous studies [78]. Lastly, future research could involve workers using their own pace in real conditions and investigation of not only the efficiency of the system, but also their opinion in order to provide a viable and socially accepted solution [6]. The following supporting information can be downloaded at [[https://drive.google.com/file/d/1](https://drive.google.com/file/d/1) qHJXW5 NFognF3 mOVRxV1y09 juVIIHb4 yz/view]([https://drive.google.com/file/d/1](https://drive.google.com/file/d/1) qHJXW5 NFognF3 mOVRxV1y09 juVIIHb4 yz/view). Video S1. Video recording from an experimental demonstration session for testing the efficacy of the proposed synergistic framework. Conceptualization, V.M., L.B. and D.B. ; methodology, V.M. and D.K. ([PERSON]); software, V.M. and D.K. ([PERSON]); validation, V.M. and A.A.; visualization, V.M. and L.B. ; writing--original draft preparation, V.M. and L.B. ; writing--review and editing, V.M., D.K. ([PERSON]), L.B., P.B., A.A., D.K. ([PERSON]), S.P. and D.B. ; supervision, D.B. ; project administration, D.B. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Ethical Committee under the identification code 1660 on 3 June 2020. Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. This research was partly supported by the Project \"Human-Robot Synergetic Logistics for High-Value Crops\" (project acronym: SYNERGIE), funded by the General Secretariat for Research and Technology (GSRT) under reference no. 2386. The authors declare no conflict of interest.