# Enhancing Robotic-Assisted Lower Limb Rehabilitation Using Augmented Reality and Serious Gaming
## 2 LegUp--Parallel Robot for Lower Limb Rehabilitation
For the flexion and extension of the knee, the q\({}_{1}\) joint is placed at a 45-degree angle and remains still, while the q\({}_{2}\) joint performs the knee joint motion. The hip-knee module contains several passive joints; the \(\alpha_{2}\) revolute joint is parallel with the sagittal plane of the hip joint and allows for hip flexion and extension. Revolute passive joints R\({}_{11}\), R\({}_{12}\), R\({}_{21}\), R\({}_{22}\), and R\({}_{k}\) allow hip-knee motions to be performed with the help of q\({}_{1}\) and q\({}_{2}\) joints. The ankle module (orange rectangle) is actuated by two active joints; prismatic joint q\({}_{4}\) performs the flexion/extension of the ankle while prismatic joint q\({}_{5}\) performs the inversion/eversion of the ankle joint. Passive revolute joint \(\gamma_{1}\) represents the rotation axis for the ankle flexion/extension motion while passive revolute joint \(\gamma_{2}\) represents the rotation axis for the ankle inversion/eversion motion. The structural dimension of the system is determined by geometric parameters such as L\({}_{t}\) (femoral length) and L\({}_{l}\) (tibial length). Geometric parameters such as L\({}_{t}\) (foot length) and \(\delta_{1}\) define the structural dimensions. Figure 3 illustrates the experimental model. The design of the hip joint includes multiple mounting points for the ankle module, enabling modifications to the tibial length and also allowing for manual adjustments to the length of the femoral segment. The system features linear ball bearings to facilitate smooth movement, along with rail and sled systems and kinematic chains with screw-and-nut mechanisms for precise linear motion. Push-pull cables and screw-and-nut mechanisms are used to operate the ankle module. Figure 2: Kinematic scheme of the LegUp robot; Hip and knee module (green rectangle) and ankle module (orange rectangle). The robot is controlled via a control interface connected to a laptop, enabling real-time adjustments and data analysis to optimize the rehabilitation process. The control module of the system, illustrated in Figure 4, consists of four main subsystems, each containing several components:  
Subsystem 1: This contains the five servo actuators of the robot that communicate with the controlling PLC using the designated encoders in order to provide data regarding the motor position, velocity, accelerations, and exerted torque on the motor. Subsystem 2: This subsystem includes all external sensors mounted on the patient, providing various types of data:  
The pulse oximeter is mounted on one of the patient's fingers and provides information about the patient's condition during rehabilitation. Besides recording vital signs and transmitting them to the patient database, the monitoring system analyzes the vital data. If anomalies are detected, it requests medical staff intervention while the parallel robot system triggers safety functions developed in collaboration with medical experts. External sensors include an integrated system mounted on the patient's hand, capable of monitoring vital signs and providing double validation of the data received from the  
Figure 4: The control architecture for the LegUp rehabilitation robot. Figure 3: Experimental model of the parallel robot and its components. pulse oximeter. Additionally, a motion amplitude measurement system is mounted on the patient's lower limbs to validate the amplitudes imposed by the robot's control. The Functional Electrical Stimulation (FES) system sends currents used for muscle electrostimulation to the processing unit during the medical rehabilitation procedure. Subsystem 3: This subsystem consists of a previously developed database that contains personal details such as age, gender, medical history, stroke history, initial evaluation, periodical evaluation, imaging analyses, a treatment plan prescribed by the doctor, biomechanical data, and the schedule for the rehabilitation session.