# Cable-Driven Exoskeleton for Ankle Rehabilitation in Children with Cerebral Palsy
## 3 Results  
To evaluate the performance of the novel ankle control module, an experimental trial was conducted with three toddlers diagnosed with cerebral palsy (CP), as follows:  
* **Participant N1**: A 4-year-old child (mass: 17 kg; height: 1.06 m), classified as Level III on the Gross Motor Function Classification System (GMFCS) [49]. This level indicates that the child walks using a hand-held mobility device and requires assistive equipment (e.g., walker or crutches), particularly for outdoor ambulation. * **Participant N2**: A 3-year-old child (mass: 13 kg; height: 0.96 m), classified as Level IV on the GMFCS [49]. This level indicates severely limited self-mobility; the child primarily relies on powered mobility or is transported in a manual wheelchair, especially for longer distances or community settings. * **Participant N3**: A 5-year-old child (mass: 17.5 kg; height: 1.15 m), classified as Level I on the GMFCS [49], indicating that the child walks without limitations but may exhibit reduced coordination or balance during more advanced motor activities such as running or jumping. The module was configured to actuate 3 DOFs relevant to sagittal plane walking: mediolateral translation (\(x\)), vertical translation (\(z\)), and _pitch_ rotation (dorsiflexion/plantarflexion). The D2W rehabilitation parameters were individually tailored to each participant's motor capabilities. Participant N1 completed 31 steps per foot on a treadmill set at 0.15 m/s, participant N2 completed 39 steps per foot at 0.10 m/s, and participant N3 completed 24 steps per foot at 0.35 m/s. For all participants, the impedance controller operated in a high-assistance mode, with a stiffness coefficient of \(K_{\mathrm{s}}=600\) N\(\cdot\)m\({}^{-1}\) and a damping coefficient of \(K_{d}=30\) N\(\cdot\)s\(\cdot\)m\({}^{-1}\). These gains were selected from the upper bound of the system's assistance range to ensure high trajectory tracking fidelity with minimal patient effort. Figure 12 presents the resulting ankle trajectories in the 3 controlled DOFs--\(x\), \(z\), and _pitch_ rotation--alongside the corresponding cable length profiles for the left ankle, for each participant. Each subplot compares the target reference trajectory with the mean of the real trajectories performed over all gait cycles. The rightmost plot in each row shows the spatial trajectory in the X-Z plane, including the reference path, all individual gait cycles, and their mean. During these trials, the ankle module operated in coordination with the pelvic and traction (treadmill) modules of the Discover2 Walk (D2W) platform. The experimental protocol was integrated into the toddlers' scheduled robot-assisted rehabilitation sessions. The ankle module was configured to follow a predefined cyclic trajectory that replicates normative ankle kinematics during gait. This trajectory involved actuation in 3 DOFs of interest. These experiments represent a pivotal step in validating the prototype by assessing the viability of the exoskeleton and ensuring both its safety and functional reliability. Table 2 summarizes the Mean Error (ME), Standard Deviation (STD), Root Mean Square Error (RMSE), Maximum Error (MaxE), and Pearson Correlation Coefficient for Tracking (TCorr) for each DOF of the three participants. Figure 12: Summary of experimental results for the three participants with cerebral palsy. From top to bottom: participant N1 (blue), participant N2 (orange), participant N3 (green), and combined results. All measurements correspond to the left ankle. Participant N1 performed 31 gait cycles, N2 performed 39, and N3 performed 24. For each subject, the left plots show the averaged ankle trajectories across all detected gait cycles for the 3 controlled degrees of freedom—\(pitch\), mediolateral position (\(x\)), and vertical position (\(z\))—as well as the commanded lengths of the eight actuation cables. The shaded regions represent the Standard Deviation across cycles.