## 5 Discussion  
As addressed above, HRC requires a seamless integration of humans and robots in a shared workspace in industry, which gives rise to new risks of worker accidents that need to be addressed. The approach to mitigate these risks is discussed including the quantification level of injury by collision. Keeping in view the environment whose main objective is to dispense safe HRC, several studies have analyzed the result of human-robot collision on the human body. This question is addressed from two different opinions, pain onset level estimation and quantifying the level of injury. This paper presents a first analysis and simulation setup to assess impact measurements and damage in the smart factory context for accidents due to HRC. However, this study is restricted to the human hand and focuses on different loading conditions on the index finger. A finite element methods approach is implemented for the simulations that are accomplished within this research. FEM is basically the discretization of spatial structures to anticipate a set of PDEs (partial differential equations) and the solution is carried out more easily with the proposed boundary conditions. To assess the impact level of severity on the human body, the FEM is widely used in the biomechanics field. A three-dimensional model of a human index finger is constructed by using 3D CAD software. The 3D model is  
Figure 14: Impact of UR10 end effector at velocity of 2.2 m/s under flexion. (**a**) Impact Geometry, (**b**) Shear Elastic Strain, (**c**) Principal Stress, and (**d**) von-Mises Stress. consisted of metacarpal phalanx, distal phalanx, and MCP joint and DIP joints. Joints are modeled as revolute joints to introduce one degree of freedom (extension-flexion). Bone is covered with soft tissue. Then, the CAD model is imported in ANSYS software, to analyze the stress distribution in the hand according to the boundary conditions provided in the ISO/TS 15066. Severity of impact is assessed based on the deep somatic pain onset level that a human can tolerate. There are various techniques available in the literature where pain onset level is studied using pinch actuators composed of pneumatic cylinders. Such cylinders can apply localized loads to various body parts to find tolerable forces. In this research, the contact force, principal stresses, and shear stresses are obtained under different loading conditions. A quasi-static analysis is first performed where a constant force not exceeding the maximum permissible force specified in ISO/TS 15066 is applied to the index finger. This results in a maximum elastic strain of 0.85 and a maximum shear stress of 5.54 MPa in the soft tissue. The maximum principal stresses developed in the bones are relatively low, at 46.3 MPa. These results provide benchmark values for shear stress and stress in soft tissue, which are used in subsequent dynamic analysis for impact. ISO/TS 15066 estimates permissible transient contact velocities using a simplified inelastic collision model. In this study, the angle, direction, and location of the impact, together with geometry and material properties of the digital hand/index finger model, are used to predict permissible robot speeds under different loading conditions for low- and medium-payload-capacity robots, and then extended to heavy-payload-capacity robots. With the ISO/TS 15066 currently under review, further research into biomechanical modeling using the FEM may pave the way for its extension to heavy-payload-capacity robots. In this study, it is observed that the results are strongly dependent on the loading conditions, i.e., the velocity, direction, and location of impact. One of the primary barriers to widespread adoption of Collaborative Robots is the perceived unsafe feeling of operators, especially for heavy-payload-capacity robots [40]. In addition to robot characteristics, factors such as the location of operators and the presence of physical obstacles add to the hazard of human-robot collaboration [41].