# Cable-Driven Exoskeleton for Ankle Rehabilitation in Children with Cerebral Palsy
## 4 Discussion  
After analyzing the results, the effectiveness of the new control module is evident: it fulfills all the design specifications. First, the module successfully guides motion in the 3 targeted DOFs--\(x\) and \(z\) translations and _pitch_ rotation. This achievement is especially noteworthy given the patient's limited voluntary range of motion and muscle strength due to his disease, specially in the case of participant N2, which has a really severe degree of CP (IV in the GMFCS scale). Despite exerting minimal force and facing physiological constraints that normally hinder the reproduction of healthy trajectories, the participant's movements remained closely aligned with the reference paths of a healthy peer of similar age and anthropometrics. The low tracking errors therefore demonstrate that the controller can compensate for residual motor deficits and reliably deliver physiologically meaningful trajectories even in patients with severe functional limitations. When interpreting the results, it is essential to remember that the system is a medical-assistive device for rehabilitation. Its primary goal is to guide the patient toward the target trajectory while still allowing the patient to exert effort and ensuring a safe physical interaction. Consequently, unlike an industrial robot, our aim is not to replicate a fixed path with sub-millimeter precision; instead, we seek to establish effective human-robot engagement that supports meaningful rehabilitation outcomes. The configuration based on four brushless motors, each driving a dual-coil drum that simultaneously winds and unwinds two cables, enabling precise control of their lengths, has proven to be an efficient way of avoiding uncontrolled ankle rotation of abductions and adductions that would occur if we used only four cables arranged in one plane. Additionally, by implementing mechanical impedance control, an AAN model has been successfully developed. This has been demonstrated in the experiments performed, as the exoskeleton has been able to direct the patient's movement towards the target trajectories, but without applying excessive forces that could be dangerous and leaving room for the patient's cooperation. Therefore, the combination of robotic action with patient activity will result in highly effective rehabilitation therapies. This project holds considerable promise, and several enhancements are already envisioned. Our primary avenue for future work will be to expand clinical validation by testing the new ankle-control module with a larger cohort of patients with cerebral palsy. Other interesting technical implementations could be to develop a new control loop, which, instead of being based on the cable length error, would be based on the end-effector position error. This could lead to a significant improvement in the accuracy of the movements, since we would control directly on the Cartesian space of the end effector and not on the joint space of the cables. Additionally, as this is an initial prototype, technical modifications will be sought in future versions to increase the precision of the movements, always with the primary objective of limiting ourselves to assisting the movement and guaranteeing a high level of safety. Although the present prototype employs mechanical impedance control within an AAN framework, emerging research indicates that bio-inspired strategies could add an extra layer of adaptability. Drawing on human motor adaptation, such controllers adjust force and impedance online to reflect the user's intent and the external environment. Biomimetic learning approaches, for example, have been shown to replicate the human ability to modulate impedance and remain stable in both predictable and unpredictable conditions without explicit force sensing [50]. Likewise, feed-forward adaptation mechanisms can enable the exoskeleton to anticipate the user's motion and counteract disturbances, thereby reducing corrective forces and promoting a more natural gait [51].