# Control Strategies for Gait Tele-Rehabilitation System Based on Parallel Robotics
## 2 Materials and Methods
### Feasibility Study  
The experiments were designed to investigate the feasibility of both proposed control strategies in terms of system performance and user subjective perception. In this section, data obtained from an individual with no gait impairments (male, 27 years old, 65 kg) is depicted. In the trial involving a therapist, another individual took part in the test (male, 34 years old, 77 kg).  
Figure 3: Control strategies for gait rehabilitation. (**a**) Represents the basic control strategy using fixed gait trajectories, and (**b**,**c**) depict the novel approaches described in this work, i.e., Therapist Modulation Mode (TMM) and Self-Modulation Mode (SMM), respectively.  
Within the experiments performed in this work, the sensors were attached either to the user trunk, where it provided upper-body flexion/extension estimates for the SMM, or to the feet, providing plantar flexion/dorsiflexion, eversion/inversion, and external/internal rotation readings for the TMM. For the latter, ideally foot position would also have to be measured and employed for controlling the SGP, but in this work only attitude was evaluated.  
Regarding the protocol, the therapist in the TMM trial and the patient in the SMM trial were told to move the orientation of their feet/trunk freely. In the TMM trial, the therapist was positioned behind the patient, as illustrated in the bottom panel of Figure 4. Although a human subject standing on the platform was not required to evaluate the system performance, we have chosen this configuration to prevent prediction of platform movement by the patient, which would possibly occur in tele-rehabilitation.  
Tele-rehabilitation feature is validated by testing interconnection between the BSU (Lima, Peru) and an RU located at Montepellier, France. The BSU and RU have a client and server TCP/IP application, respectively, which allow sending commands to the SGP and requesting data from wireless inertial sensors. Public IPs are assigned to both BSU and RU computers. An initial testing using the \"ping\" command is conducted to assess the typical delay transmitting and receiving data packets during the experiment. No virtual private network nor dedicated internet connection is used in this experiment. Once the sanity check is done, a TCP/IP port is open in both computers to establish communication. Command transfer and SGP data queries were conducted between 5:00 to 7:00 pm, Montpellier local time, to evaluate the performance requirements during peak hours.  
After the experiments, the simulated participant filled a questionnaire to evaluate his experience. Since no standard instrument to evaluate the usability of such a type of system was found, a customized form composed of open questions was applied.  
Figure 4: Experimental data from an TMM trial. Top panel shows data from the sensors, which are used to compute the piston displacement reference shown in the center panel. Bottom panel shows two figures that serve to illustrate two distinct instants from the trial. The therapist, using the wireless inertial sensors, input desired set of movements to the mechanical system that are replicated and transmitted to the patient (over the SGP). The tele-rehabilitation feature of the system allows the therapist to conduct this procedure from a remote location.