## 7 Discussion  
A comparison between the experimental results and the results obtained by numerical simulation in MSC.ADAMS, presented in Figure 14, has been made. Therefore, it was observed that the maximum value of the moment necessary to operate the flexion/extension module is 147.37 Nm experimentally, and by numerical simulation in ADAMS we obtained the value of 149 Nm. The negative value recorded in the experimental torque determination comes from the calibration of the torque-recording transducer, with the maximum value being recorded in the negative direction of the axis. MSC.ADAMS shows the absolute, and therefore positive, value of the torque. As a result, in absolute terms, the difference between the maximum experimental value and that obtained by simulation is 1.63 Nm, i.e., less than 1%.  
For the moment necessary to operate the adduction/abduction module, we obtained experimentally the maximum moment value of 14.4 Nm, and by numerical simulation in MSC.ADAMS we obtained the value of 25 Nm. It is observed, however, in this case that the allure of the variation curve of the moment obtained by simulation is similar to that obtained experimentally.  
A similar approach and the obtained results are presented in previous papers [45] with reference to a dynamic study of a robotic system for lower limb rehabilitation.  
In a preliminary study with finite elements of the robot modules, the conclusion is that high stresses appear in the assembly parts of the elements. The optimization of these assemblies was realized by introducing the fillet radius and chamfering the sharp edges. In this way, the maximum stresses decreased from 123 MPa to 64.271 MPa.  
Thus, the structural strength of the flexion/extension module was checked in ANSYS FEA software. The kinematic and dynamic parameters of the optimized version of the ASPIRE robot mounted on a virtual mannequin that respects the anthropometric data of a user are studied, considering the component elements as being deformable.  
Figure 24: The torques required to operate the ASPIRE robot, measured experimentally [43].  
The numerical simulation in MSC.ADAMS should consider the real aspects of the operation, such as friction and deformability of the elements, to obtain results as close as possible to the real situation. To obtain an improved variant of the robot, studies are performed on optimizing the shape and constructive structure of the robot that improves the mechanical strength and dynamic behaviour and leads to the increased stability of the movement of the robot system--the human arm.  
The difference between the experimentally recorded maximum values and those obtained by simulation comes from the parameters introduced in the MSC.ADAMS simulation, which may differ from the actual operating conditions. However, the similar allure of variation of the torques obtained experimentally and those obtained by numerical simulation in MSC.ADAMS can be noticed. The results are similar when comparing between the torques measured experimentally and those obtained by numerical simulation in MSC.ADAMS in the case of considering the deformability of the elements.  
Additionally, the differences that appear between the experimental results [43] and those obtained by numerical simulation in MSC.ADAMS are explained by the manufacturing tolerances of the parts, as well as the assembly tolerances, which are responsible for the different elasticity of the real robot modules compared to the one considered in the simulation. Moreover, in the simulation, the modules were considered as a unitary assembly, united by fixed couplings. In reality, these elements are joined by removable assemblies, which offer a slightly different elasticity. Nonetheless, there is a clear similarity of the mode of variation for the operating moments of the modules obtained by numerical simulation and experimental determination.