# Enhancing Robotic-Assisted Lower Limb Rehabilitation Using Augmented Reality and Serious Gaming
## 2 LegUp--Parallel Robot for Lower Limb Rehabilitation  
The necessity for a wide range of rehabilitation systems has driven researchers and medical professionals to develop innovative and cost-effective robotic solutions, aimed at assisting people from diverse social backgrounds [26; 27], with a focus on different stages of the rehabilitation process. One such system is the LegUp parallel robot introduced in [28]. It was developed to address a gap in lower limb rehabilitation, specifically for bedridden patients (e.g., those recovering from stroke, spinal cord injuries, or major surgeries such as hip or knee replacements), who require early physical rehabilitation to achieve maximum therapeutic outcomes. LegUp is a 5-Degree-of-Freedom (DOF) parallel robot designed for spatial rehabilitation of the lower limb. LegUp involves the movement of the hip and the ankle in both the sagittal and coronal planes and the knee in the sagittal plane. To enable a simple and fast alignment with the anthropometric characteristics of the patients, the parallel robot has a modular construction, with one module for the rehabilitation of the hip and knee and a module for the ankle joint. The robot design enables the alignment with most hospital beds supporting its use in the hospital for multiple pathologies. The robot's parallel structure contributes to its stiffness, which enhances precision and ensures safety, making it well suited for rehabilitation applications. The movements targeted by the LegUp during the lower limb rehabilitation process are illustrated in Figure 1. The amplitudes for these motions were previously established based on the joint movement measurements taken from healthy subjects, as summarized in Table 1.  
The range of motion for hip flexion and extension is between 0\({}^{\circ}\) and 30\({}^{\circ}\), while the hip abductions and adduction range from 0\({}^{\circ}\) to 30\({}^{\circ}\). Knee flexion and extension occur between 0\({}^{\circ}\) and 90\({}^{\circ}\) and are performed with a hip flexion set between 20\({}^{\circ}\) and 30. Ankle flexion and extension range from \(-\)20\({}^{\circ}\) to 10, while ankle inversion/eversion varies from 0\({}^{\circ}\) to 10\({}^{\circ}\). Together, hip and knee flexion and extension operate with \(\pm\)10\({}^{\circ}\) compliance for the knee, while ankle flexion and extension, combined with inversion and aversion, involve rotational motion with \(\pm\)10\({}^{\circ}\) compliance for both the hip and knee. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Joint** & **Motion** & **Range of Motion** \\ \hline Hip & Flexion/Extension & 0\({}^{\circ}\) to 30\({}^{\circ}\) \\ Hip & Abduction/Adduction & 0\({}^{\circ}\) to 30\({}^{\circ}\) \\ Knee & Flexion/Extension & 0\({}^{\circ}\) to 90\({}^{\circ}\) \\ Ankle & Flexion/Extension & \(-\)20\({}^{\circ}\) to 10\({}^{\circ}\) \\ Ankle & Inversion/Eversion & \(-\)10\({}^{\circ}\) to 10\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Range of motion limits for each joint. Figure 1: The movements targeted by the LegUp parallel robot in lower limb rehabilitation treatment. The kinematic scheme of the robot is shown in Figure 2. The robot has two main modules: a hip-knee module and an ankle module. The hip-knee module (green rectangle in Figure 2) is composed of three active joints; revolute joint q\({}_{1}\) performs the hip abduction-abduction motion by revolving the entire kinematic mechanism around the OX axis, and the revolute axis of this joint is perpendicular to the patient coronal plane when the patient is laid on his back. The prismatic joints q\({}_{1}\) and q\({}_{2}\) are responsible for executing the flexion/extension on the hip and the flexion extension of the knee, respectively. For performing the flexion and extension of the hip, the two joints have to move in a synchronized manner in order to rotate the hip of the patient around the OY axis without modifying the knee joint angle.