## 4 Dynamic Analysis of the ASPIRE Robot Using MSC.ADAMS Software
### Dynamic Analysis in MSC.ADAMS of the Robot, Considering the Kinematic Elements as Rigid Solids
The fact that the values of the resulting reaction along the X axis are negative is again natural, because the component of the connecting force along the X axis acts downwards and has the opposite direction to the axis of the local reference system attached in the rotation torque B. In conclusion, according to the results obtained for the connecting forces in couplings A and B, it results that the flexion/extension module is subjected to the highest mechanical stresses. It is therefore necessary to verify its structural integrity with the finite element method, a verification that will be performed later in ANSYS. Dynamic Analysis in MSC_ADAMS of the Robot, Considering the Rigid Solid Kinematic Elements and the Friction in the Couplings  
The previously presented results for the actuation moments and the connection forces from the kinematic couplings are obtained by numerical simulation in MSC_ADAMS in the simplifying hypothesis, by which the frictions from the kinematic couplings were not taken into account. In reality, the presence of friction in the couplings imprints another character on the dynamics of the ASPIRE robot. For these reasons, in the second phase, we will consider the frictions that appear in the kinematic couplings A, B and C. The parameters necessary for defining the frictions in the kinematic couplings are defined according to the data from Figure 13, for the definition of which the existing data in the literature were taken into account [54]. According to the existing data in the specialized literature, we adopted for the static friction coefficient the value of 0.3, and for the dynamic friction coefficient, we specified the value 0.2. Figure 12: Connecting forces in the rotating coupling B, connected to the base, of the flexion/extension module: (**a**) on x direction; (**b**) on y direction; (**c**) on z direction; (**d**) resultant. The results obtained by numerical simulation in ADAMS, where the friction in the kinematic couplings of the ASPIRE robot is considered, are presented below. The laws of variation of the moment necessary to operate the flexion/extension module, as well as the abduction/adduction module, are presented in Figure 6:0  
There is an increase in the motor torque required to operate the modules in this case, as well as a steeper variation, similar to that determined experimentally [43]. The results obtained for the connection forces from the kinematic couplings in the hypothesis of considering the friction from the robot joints are presented below. Figure 15 shows the graphs obtained for the variation laws of the connection forces for the coupling A, calculated in the simulation from ADAMS. If we compare these results with those shown in Figure 11, in which case we did not consider the friction in the kinematic couplings, it is found that we have an increase in the connecting forces. Thus, the component along the X axis of the connecting force shows an increase from the value of \(-36\) N to a maximum value of \(-70\) N (Figure 15a). In the case of the connecting force component along the Y axis, the increase occurs from 23 N to 70 N (Figure 15b). There is also an increase in amplitude from 20 N to 100 N. The component of the reaction along  
Figure 6:1 Second setup ADAMS simulation computed torque for: (**a**) the flexion-extension module; (**b**) the adduction-abduction module. Figure 6:2 Parameters defining the friction force in the ASPIRE robot couplings. the Z axis shows an increase from \(-271\) N to \(-285\) N (Figure 15c). The maximum value of the reaction resulting from the coupling A increases from the value of 274 N to 284 N. It is also found that the presence of friction in the couplings imposes a more dynamic character of the movement, an aspect which is highlighted by the steeper variation of the variation graphs. For coupling B, the connecting forces obtained in Figure 16 are presented in the case of considering the friction in couplings. There is also an increase in the maximum values obtained, assuming the friction of the couplings.