## 4 Discussion  
This study developed an MGTR that used walking speed to link to a VR system, including a biofeedback system that used step length to control the lower limb joint angle. By adjusting step length according to the speed, it aided in the implementation of a normal gait trajectory for patients with gait problems. Development and performance tests were performed for each element of the device. The durability was revealed to be four times the maximum allowable load; the contraption also passed the 100,000-cycle load test, with a load applied to each step plate. Noise generated during the operation was measured at 68.9 dB. Results of the stability and durability tests offered assurance of patient safety while boarding. As the results of the gait trajectory have been verified in previous studies, additional verification was not performed [20]. In the performance test for the VR system, the error rate when matching the gaze and angle was confirmed to be less than 1%. The resolution of the operating system and VR were estimated to be 690 and 118 fps, which guarantees an acceptably immersive experience during the rehabilitation exercise [21]. The angles of the hip and knee joints increased with step length at a speed of 1 km/h; this change was not observed in the ankle joints. This demonstrates that joint angle can be controlled by adjusting the step length. The performance of the joint control equipment of the robot-assisted gait training device for orthopedic exercise was measured. According to the medical device guidance from the Ministry of Food and Drug Safety and Korean standard for medical treadmill (KS P 8405:2007) [22], it should be at least 25 \(\pm\) 5\({}^{\circ}\), 40 \(\pm\) 5\({}^{\circ}\), and 20 \(\pm\) 5\({}^{\circ}\) for the hip, knee, and ankle joints, respectively; this experiment showed that the angles for these three joints were at least 27.4\({}^{\circ}\), 41.7\({}^{\circ}\), and 32.9\({}^{\circ}\), respectively. Therefore, the requirements for gait training equipment were satisfied. In general, the average RoM in normal gait is approximately 40\({}^{\circ}\), 60\({}^{\circ}\), and 30\({}^{\circ}\) for the hip, knee, and ankle joints [23]. The average RoM of the hip, knee, and ankle joints in Lokomat, a representative exoskeletal MGTR (Hokoma Inc., Zurich, Switzerland), were 45.6\({}^{\circ}\), 60.3\({}^{\circ}\), and 29.2\({}^{\circ}\)[24], while those of the MGTR developed in this study were 32.4\({}^{\circ}\), 47.6\({}^{\circ}\), and 36.6\({}^{\circ}\), respectively; however, it was confirmed that the joint flexion and extension conformed to the standards of the training equipment. Because the joint ROM is different depending on the patient's movement function and muscle strength, it is possible to set up a program that sets the step length according to the patient's condition and gradually increases it during training. In the previous study, the hip and knee joint angles were compared between ground walking and passive (patient active) walking at MGTR [20]. Direct comparison and statistical analysis with this study results are difficult because the conditions of the subjects in this study are different. Therefore, the maximum and minimum angles and range of motion of the knee and hip were compared intuitively (Table 3). As a result, it can be seen that the minimum and maximum joint angle and range of motion measured by the occupant of the motor active MGTR are relatively similar to ground walking than the passive MGTR. This is considered to be the influence of a load and a force generated by the user according to the actuator's walking guidance. Therefore, it is thought that motor active mode will be more advantageous for patients whose purpose is to learn normal gait patterns. The effect in actual patients is planned to be confirmed through clinical studies in the future.