# Cable-Driven Exoskeleton for Ankle Rehabilitation in Children with Cerebral Palsy
## 1 Introduction
Although still under simulation, the system has demonstrated strong potential in terms of control accuracy and future clinical applicability. Probably, the system most comparable to the exoskeleton presented in this paper is the one developed by [PERSON] et al. [37; 38]. This cable-actuated exoskeleton, developed over the last decade, is built upon a prismatic frame with motors anchored to it, which actuate cables to assist ankle motion during the swing phase in adult patients with incomplete spinal cord injury. The system aimed to increase walking speed and endurance, and included a pelvic support structure for partial body weight unloading. Ankle guidance was provided via two cables per leg. After several weeks of rehabilitation sessions, the system demonstrated substantial potential to enhance walking ability in the tested participants. This paper presents a novel CDPR-based exoskeleton for gait rehabilitation in children with CP. The project is based on the Discover2 Walk (D2W) exoskeleton (see Figure 1) [39], a modular, cable-actuated robotic platform designed for pediatric gait rehabilitation in the early stages of CP. As an end-effector-type robot, The D2W transmits forces from distal interfaces via lightweight cables to the patient's joints, rather than placing actuators directly at the joints [26]. This innovative design enables young children to develop mobility and explore their surroundings at an age comparable to their peers without CP [39]. Within the D2W exoskeleton, we will focus on the design and implementation of a new ankle control module. The system consists of four brushless motors, each driving a dual-coil drum that simultaneously winds and unwinds two cables, enabling precise control of their lengths and end-effector position. The main motivation behind the design of the new ankle control module is to develop a new configuration that allows for controlling 3 DOFs: 2 translational (Cartesian \(x\) and \(z\) axes) and 1 rotational (_pitch_ rotation in Euler angle notation). This represents an improvement over the original D2W system, which was only capable of controlling translational motions. The implementation of the new system is due to feedback from clinicians associated with the D2W project, who highlighted the importance of being able to control dorsiflexion and plantarflexion rotations (_pitch_ rotation). The objectives pursued by the new ankle control module are the following:  
* Develop a new ankle control module that is capable of guiding ankle movement in 3 DOFs (\(x\) and \(z\) translations and _pitch_ rotation) by mimicking healthy human gait patterns. * Make sure to restrict unwanted abduction and adduction rotations of the ankle (lateral rotation of the ankle). * Ensure the modular character of the exoskeleton for easy implementation and communication with the global D2W system. * Implement the Assistance-as-Needed (AAN) model that combines robotic actuation with the patient's effort and ability to move for the correct performance of movements during rehabilitation (to be detailed more specifically in Section 2.2.4). * To carry out the experimental validation of the prototype with a CP patient to ensure its safety and ability to guide the movements of interest. This would lead, if successful, to the start of the clinical validation process of the prototype. The main contribution of this paper is the development and validation of a novel cable-driven exoskeleton for ankle rehabilitation in children with CP. This exoskeleton, integrated within the D2W modular robotic platform, introduces an innovative ankle control module capable of guiding ankle motion in 3 degrees of freedom: 2 translational (\(x\) and \(z\) Cartesian directions) and 1 rotational (dorsiflexion and plantarflexion).