# Trends of Human-Robot Collaboration in Industry Contexts: Handover, Learning, and Metrics
## 1 Introduction  
The industry world uses many automation systems to achieve massive production by the repeatability that it allows. However, traditional robotic systems are not suitable for every task that each production requires. There are some tasks that involves uncertainties and demand cognitive knowledge, that only humans can provide, to successfully complete them. Contrarily, humans do not have the same speed, stamina and physical strength as robots do. This duality leads to an idealization of a co-working between humans and robots in a way that both of the contributors could make use of their own values and not be limited by their own conditions. This combination of working is addressed as Human-Robot Collaboration (HRC).  
In [1], numerous applications of robots within human lives are presented, involving topics such as elderly, bio-feedback system, schools and learning, medicine, entertainment, space exploration and military. Several studies and research works were recently developed contributing to the progress of this research field. The work of [PERSON] et al. [2] shows the remarkable growth of publications between the years 1996 and 2015 regarding the topic of Human-Robot Collaboration. As expected, each robotic researcher provides a subjective consideration about HRC. For example, [PERSON] et al. [3] sustain that a collaborative robotshould improve the quality of task execution, ensure safety for the human user and be ergonomic for this same human co-worker. According to [PERSON] et al. (2018), HRC translates a balance between automation and flexibility, aiming to respond to the demands of the market in terms of product customization, variability, and cycle time. These different perspectives fall on the distinct levels that the HRC domain enclose.  
There are several research challenges that need to be addressed in the study of collaborative processes that are at the intersection of robotics, engineering, Human-Robot Interaction, and computer science. Collaborative robots need to be endowed with a set of abilities that enable them to act in close contact with humans, such as sensing, reasoning, and learning. In turn, the human must be placed at the centre of a careful design where safety aspects and intuitive physical interaction need to be addressed as well. Industrial applications impose additional concerns since the robots need to be easily programmed by non-expert users, while operating in poorly structured, dynamic environments. The development of intuitive and natural communication interfaces requiring little training and capable of maintaining low levels of fatigue is a priority, including those associated with direct physical interaction.  
Considering the ultimate goal of a fluent, human-like and flawless collaboration, we realize the existence of a wide range of topics that need to be completely covered up, such as safety, interaction, physicality, cognition, adaptation, metrics, among many others. Figure 1 provides a hierarchical representation of some of the fundamental topics associated with HRC, giving a special emphasis to the following research trends: better interaction, cognitive integration, and effective metrics. Despite the continuous advances, new techniques for improved functionalities need to be developed with safe physical interaction in mind and validated in industrial scenarios.  
Figure 1: Mind map of the Human-Robot Collaboration paradigm.