# Human-Robot Interaction for Improving Fuselage Assembly Tasks: A Case Study
## 2 Human-Robot Interaction and Regulatory Frameworks
#### From ISO 10218 to ISO/TS 15066:2016  
Currently, this specification is the most detailed document which gives guidelines about safety requirements in the field of collaborative industrial robot work cells and it is mainly focused on mechanical risk.  
According to the specification, to ensure a safe collaboration among human workers and robot systems, mechanical risks must be minimized in order to avoid unexpected contacts in terms of gravity and/or probability. ISO/TS 15066 introduces four different methods for safe HRI: _Safety-rated monitored stop_ which provides for the stop of robot motion when an operator enters the collaborative workspace. Then, only when the operator leaves the zone, the robotic task can automatically resume. _Hand guiding_ method takes into account the operator that is able to fully control the robot motion by direct physical interaction. Hence, the operator can guide manually the robotic task, simply by moving the robotic arm by mean of a tool located at or near the end-effector. The operator can enter in the collaborative working zone only once the robot has achieved a safety-rated monitored stop condition. For the speed and separation monitoring_ method, the speed and distance among human and robots must be continuously monitored by means of a control system. Thus, the robot is able to dynamically maintain a correct combination of speed and distance in order to avoid the possibility of any hazardous motion which may be the cause for unexpected contacts.  
The last one is _power and force limiting_ in which the biomechanical risk of unexpected human-robot contacts is sufficiently reduced either through inherently safe means in the robot or through a safety-related control system [35].  
Since the case study here-in presented falls within the speed and separation monitoring context, some additional information is provided below.  
In particular, the protective separation distance (S\({}_{p}\)), defined in Equation (1), is a function f(.) of:  
* the robot-system reaction time (\(T_{r}\)): the time required for detecting the operator, elaborating the signal and activating the stop;
* the stopping time of the robot (\(T_{s}\)): the time among the start of stop signal and the instant in which the robot halts;
* the speed of the human worker in direction of the robot's moving tool (\(V_{h}\));
* the speed of robot in course of stopping (V\({}_{s}\)): the time between the stop signal activation and the real stopping instant;
* the intrusion distance (\(C\)): the distance that a part of the body can intrude into the sensing area of the robot before it is detected;
* the position uncertainty of the operator in the shared workspace (\(Z_{d}\)) and the position uncertainty of the robot system (\(Z_{r}\)):  
\[S_{p}=\text{f}(T_{r},\,T_{s},\,V_{h},\,V_{s},\,C,\,Z_{d},\,Z_{r}) \tag{1}\]  
Thus, while the ISO 10218 describes in general terms the 4 types of collaborative operations, ISO 15066 adds new information to improve the design criteria of a collaborative system. Although not normative, the technical specification accurately describes the state of the art of safety of collaborative actions and provides specific guidance for risk assessment. ISO 10218, which focuses on industrial robots in general, leaves room for ISO/TS 15066, which focuses on collaborative robots and the definition of requirements to ensure the safety of production operators interacting with robotic systems. A further step forward is the presence of data on injury levels through the identification of pain thresholds in the different parts of the body in contact with the robot and the related force and pressure levels that lead to the improvement of the design of the systems avoiding the exceeding of these thresholds in case of human-robot contact.