Lower extremity exoskeletons for gait rehabilitation of motor-impaired patients

Robotic rehabilitation for physical therapy has several advantages over conventional manual rehabilitation, especially in the aspects of accuracy and repeatability. Initial attempts at robotic rehabilitation focused on training muscles by moving limbs in a fixed repetitive pattern. Later it was realized that such an approach could be suboptimal. Better approach would be the use of 'assist-as-needed' paradigm, where an orthotic device provides just enough assistance to enable the patient to move his leg under his own control. However, at this time, lower extremity devices which can apply appropriate forces to implement this paradigm are still in research and not commercially available. The goal of this work is to develop lower extremity orthotic devices using assist-as-needed paradigm for robotic rehabilitation. To achieve this goal two orthotic devices were developed. They are Gravity Balancing leg Orthosis (GBO) and Active Leg EXoskeleton (ALEX).;GBO assists persons with hemiparesis to walk by reducing or eliminating the effects of gravity on the affected limb. The amount of assistance provided can be tuned by the therapist from 0% to 100% gravity balancing. For a quantitative evaluation of the performance of the device several experiments were conducted. These experiments were performed on five healthy subjects and three stroke patients. The results showed that with the GBO set to 100% balancing the EMG activity from the rectus femoris and hamstring muscles was reduced by 75%, during static hip and knee flexion, respectively. For leg-raising tasks the average torque for static positioning reduced by 66.8% at hip joint and 47.3% at knee joint, however if transient portion of the leg raising task is included, the average torque at hip reduced by 61.3% and at knee increased by 2.7% at knee joints. In the walking experiment there was a positive impact on the range of movement at the hip and knee joints, especially for stroke patients, the range of movement increased by more than 57% at hip joint and by more than 73% at the knee joint. These results show that the GBO provides assistance which can be used for rehabilitation. An intensive training of a stroke patient was performed to study the long term effects of GBO, the training lasting for six weeks. The training started out with maximum assistance of 100% gravity balancing and gradually reduced to 0% by the end of training. Patient is also shown visual display of his gait pattern in real time and summary performance after individual sessions. Some of the effects of the training were, increase in patients preferred speed of treadmill walking from 2.72 km/h to 3.04 km/h, patient's preferred overground speed increased from 3.38 km/h to 3.86 km/h by the last evaluation. An improvement of gait pattern was seen where the patients gait pattern became more like a healthy subject's pattern. The patient was able to increase weight bearing on the hemiparetic leg and was more symmetric in his walk.;ALEX, on the other hand, is a motorized orthotic device. To achieve the goal of 'assist-as-needed' paradigm for ALEX, Force-Field controller was developed. This controller generates "virtual walls'' in the plane containing human thigh and shank segments. These virtual walls guide and assist the subject's foot along the prescribed trajectory. Linear actuators were used at hip and knee joints of the device. To make the actuators back-drivable, friction compensation was used. Gait training studies with healthy subjects were conducted to measure the effectiveness of ALEX in retraining modified gait pattern. The results show that a healthy human leg muscles can be trained in about 45 to 60 minutes to a modified pattern of foot trajectory. A 15-day long gait training was conducted with a stroke patient using ALEX, the results indicate that using ALEX and force-field controller, the patient's gait pattern improved significantly in many aspects. His gait speed improved both on treadmill from 1.45 km/h to 2.57 km/h and overground from 1.82 km/h to 2.50 km/h. His foot trajectory increased and got about 85% closer to a healthy subject's foot trajectory. Knee flexion increased from 27.2 deg to 47.5 deg and ankle dorsi-flexion increased from 1.9 deg to 5.9 deg by the end of the training.;All these results indicate that by using these devices suitably and implementing a long term gait training can help patients with walking disability in a speedy recovery.