*7.2. Discussion*

The numerical simulation analysis, regarding Test 1, obtained from Figure 5 confirms that the designed control technique of this study is able to track a defined position of both WRK links (thigh and calf) with zero steady-state error in the free load test. On the other hand, in Figure 6, the speeds of the WRK links (thigh and calf) are tracked with zero steady-state error. In both the position and velocity tracking, the robustness is adaptively achieved by the proposed controller against model errors and external disturbances.

According to the findings shown in Figures 9–12, the controller was able to successfully monitor the appropriate position and speed of the calf and the thigh. When it came to position monitoring, however, there was a small delay between the real location and the position. It is reasonable to anticipate that this takes place, given that the delay was not taken into account. As a consequence of the calf link, the controller was in a position to track the necessary speed with satisfactory outcomes. The thigh link's tracking speed had a error term due to the fact that in this study we exclusively focused on the robustness and adaptiveness of the system to random external disturbances, as shown by Equations (54) and (55). Upon retesting, the controller consistently provided the same performance results. The adaptability and robustness of the controller to different user parameter combinations in Tests 4 and 5 resulted in the same performance as in tests 2 and 3. As a consequence of these tests, it has been noticed that there is a delay in response when tracking the positions of calf and thigh links (Figures 14 and 17), as well as errors in tracking thigh link speed (Figures 15 and 18). Additionally, it has been observed that there is a delay in response when tracking the angle of rotation of the thigh link (Figures 14 and 17). The controller designed in this paper achieves asymptotic tracking even in the presence of unstructured disturbances. It should however be noted that high control gains may lead to inappropriate responses, including inadmissible overshooting. Thus, in order to limit such high controller gains, an adaptive controller is included that reduces tracking error and overshoots. The input torques for the thighs and calves of persons 3 and 4 are represented in Figures 16 and 19, respectively. The hard motional dynamics constraints considered in the output trajectories show that the stability of the controlled closed loop system was achieved and the dynamical behavior is quite satisfactory. The RBF NN proved its efficiency in compensating for all model uncertainties and random external disturbances. The remaining three tests confirm the ability to apply the designed controller to users with different physical parameters (height, weight and gender). The proposed controller was designed for both males and females with different user parameters (thigh length and mass, calf length and mass) that differ slightly according to biological features, as described in [20,21]. Thus, the controller was adaptive to the potential physical parameters of users and robust to external unstructured disturbances.
