# Hardware Development and Safety Control Strategy Design for a Mobile Rehabilitation Robot
## 5 Experimental Validation
### Using the MRR for Over-Ground Gait Training  
The MRR can guide and help subjects to perform over-ground walking. However, when walking, the subject's posture and center of the mass are variable while wearing the  
Figure 12: Right knee joint trajectory tracking for LES with the ILESO\(-\)PSMC. (**a**) Knee joint angle tracking response; (**b**) knee joint angle tracking error; (**c**) current control signal.  
Figure 13: Right hip joint trajectory tracking for LES with the ILESO\(-\)PSMC. (**a**) Hip joint angle tracking response; (**b**) hip joint angle tracking error; (**c**) current control signal.  
LES; therefore, it is challenging to maintain a stable unloading force while wearing the LES. The designed MRR provides subjects with stable and robust bodyweight unloading force during ground gait training. The third experiment was performed to decide the availability of the MRR adopting to an ILESO-PSMC. The AMBSS was controlled to lead a subject to walk forward at a set speed. In the experimental evaluation, a healthy male subject with a height of 1.7 m and a weight of 70 kg without a history of disability was used. The bodyweight unloading force for the AMBSS was set to 20% weight reduction of the user's body weight. The complete gait cycle for the LES was set to 5 s. The control parameters of the gait training experiment are listed in Tables 1 and 2. During the first 30 s, AMBSS progressively increased the bodyweight unloading force to 20% of the subject's body weight. After reaching the set bodyweight unloading force, the AMBSS cooperated with the LES and moved forward at a gait speed of 5 s for repeated over-ground gait training. The LES enabled over-ground gait trajectory tracking control, and the AMBSS started to execute bodyweight support control. The unloading force target was 20% (137.2 N) of the subject's body weight. Figure 14a shows that the AMBSS slowly and comfortably reached an unloading force of 20% of the subject's body weight within 30 s. The bodyweight unloading force tracking error in the first 30 s was within the interval of (\(-\)12, 18) N. The movement of MRR made it difficult to control the bodyweight unloading force; therefore, the bodyweight unloading force tracking error increased to an interval of (\(-\)22, 30) N at 30-85 s. Figure 14c presents the PWM control signals of the AMBSS, which are regarded as duty cycles. The maximum signal values appeared in the over-ground gait training stage, i.e., during the tautening and relaxing of the harness, causing the maximum tracking error in the walking stage (Figure 14b). Clearly, the ILESO-PSMC was effectively able to bound the tracking errors. Figures 15a and 16a display the trajectory-tracking performance of the right hip and knee joints during the CPM gait trajectory tracking process, respectively. Figures 15b and 16b illustrate the angle trajectory tracking error of the knee and hip joints during CPM gait trajectory tracking, respectively. During over-ground CPM gait trajectory tracking, the angle tracking errors of the knee and hip were about \(\pm\)0.6\({}^{\circ}\) and \(\pm\)1\({}^{\circ}\), respectively. Figures 15c and 16c indicate the control current of the ILESO-PSMCs for the knee and hip. The performance of bodyweight support control and over-ground gait trajectory tracking control deteriorated due to coupling effects.  
Figure 14: Dynamic bodyweight unloading force control of ILESO\(-\)PSMC, 20% (137.2 N) of participant body weight (686 N). (**a**) Unloading force tracking response; (**b**) unloading force tracking error; (**c**) duty cycle of PWM.  
Figure 16: Right knee joint trajectory tracking for LES during the overground gait training with the ILESO\(-\)PSMC. (**a**) Knee joint angle tracking response; (**b**) knee join angle tracking error; (**c**) current control signal.  
Figure 15: Right hip joint trajectory tracking for LES during the overground gait training with the ILESO\(-\)PSMC. (**a**) Hip joint angle tracking response; (**b**) hip joint angle tracking error; (**c**) current control signal.