Sai K. Banala

Gravity-Balancing Leg Orthosis and Its Performance Evaluation

In this paper, we propose a device to assist persons with hemiparesis to walk by reducing or eliminating the effects of gravity. The design of the device includes the following features: 1) it is passive, i.e., it does not include motors or actuators, but is only composed of links and springs; 2) it is safe and has a simple patient-machine interface to accommodate variability in geometry and inertia of the subjects. A number of methods have been proposed in the literature to gravity-balance a machine. Here, we use a hybrid method to achieve gravity balancing of a human leg over its range of motion. In the hybrid method, a mechanism is used to first locate the center of mass of the human limb and the orthosis. Springs are then added so that the system is gravity-balanced in every configuration. For a quantitative evaluation of the performance of the device, electromyographic (EMG) data of the key muscles, involved in the motion of the leg, were collected and analyzed. Further experiments involving leg-raising and walking tasks were performed, where data from encoders and force-torque sensors were used to compute joint torques. These experiments were performed on five healthy subjects and a stroke patient. The results showed that the EMG activity from the rectus femoris and hamstring muscles with the device was reduced by 75%, during static hip and knee flexion, respectively. For leg-raising tasks, the average torque for static positioning was reduced by 66.8% at the hip joint and 47.3% at the knee joint; however, if we include the transient portion of the leg-raising task, the average torque at the hip was reduced by 61.3%, and at the knee was increased by 2.7% at the knee joints. In the walking experiment, there was a positive impact on the range of movement at the hip and knee joints, especially for the stroke patient: the range of movement increased by 45% at the hip joint and by 85% at the knee joint. We believe that this orthosis can be potentially used to design rehabilitation protocols for patients with stroke

Assessment of Motion of a Swing Leg and Gait Rehabilitation With a Gravity Balancing Exoskeleton

The gravity balancing exoskeleton, designed at University of Delaware, Newark, consists of rigid links, joints and springs, which are adjustable to the geometry and inertia of the leg of a human subject wearing it. This passive exoskeleton does not use any motors but is designed to unload the human leg joints from the gravity load over its range-of-motion. The underlying principle of gravity balancing is to make the potential energy of the combined leg-machine system invariant with configuration of the leg. Additionally, parameters of the exoskeleton can be changed to achieve a prescribed level of gravity assistance, from 0% to 100%. The goal of the results reported in this paper is to provide preliminary quantitative assessment of the changes in kinematics and kinetics of the walking gait when a human subject wears such an exoskeleton. The data on kinematics and kinetics were collected on four healthy and three stroke patients who wore this exoskeleton. These data were computed from the joint encoders and interface torque sensors mounted on the exoskeleton. This exoskeleton was also recently used for a six-week training of a chronic stroke patient, where the gravity assistance was progressively reduced from 100% to 0%. The results show a significant improvement in gait of the stroke patient in terms of range-of-motion of the hip and knee, weight bearing on the hemiparetic leg, and speed of walking. Currently, training studies are underway to assess the long-term effects of such a device on gait rehabilitation of hemiparetic stroke patients.

Novel Gait Adaptation and Neuromotor Training Results Using an Active Leg Exoskeleton

The gait of every adult is unique and expected to be ingrained within the neuromuscular system. The major scientific question that we ask in this paper if it is possible to alter the gait of healthy individuals using special purpose design of robots and training paradigms. This paper describes novel experimental results with an active leg exoskeleton (ALEX) and a force-field controller (FFC) developed for neuromotor training of gait and rehabilitation of patients with walking disabilities. ALEX is a motorized leg orthosis having a total of 7 DOFs with hip and knee actuated in the sagittal plane. The FFC applies forces on the foot to help the leg move on a desired trajectory. The interaction forces between the subject and the orthosis are designed to be ¿assist-as-needed¿ for safe and effective gait training. Simulations and experimental results with the FFC are presented. Experiments have been performed on six healthy subjects walking on a treadmill. It was shown that a healthy subject could be retrained in about 45 min with ALEX to walk on a treadmill with a considerably altered gait. In the coming months, this powered orthosis will be used for gait training of stroke patients.

A Powered Leg Orthosis for Gait Rehabilitation of Motor-Impaired Patients

This paper describes a powered leg orthosis for gait rehabilitation of patients with walking disabilities. The paper proposes controllers which can apply suitable forces on the leg so that it moves on a desired trajectory. The description of the controllers, simulations and experimental results with the powered orthosis are presented in the paper. Currently, experiments have been performed with a dummy leg in the orthosis. In the coming months, this powered orthosis will be used on healthy subjects and stroke patients.

Design and Optimization of a Mechanism for Out-of-Plane Insect Winglike Motion With Twist

A mechanism is presented that can generate insect winglike motion. This motion includes both flapping out of the stroke plane in addition to twist of the wing. The mechanism has a single degree of freedom and employs a five-bar mechanism in addition to an auxiliary four-bar mechanism. The parameters in the mechanism were optimized to generate a prescribed motion of the wing taken from a hawk moth kinematic flight data. A scaled model of the mechanism was fabricated to verify practical feasibility of the design. In future, we will miniaturize this mechanism on our flying-bird prototypes.

Design of a two degree-of-freedom ankle-foot orthosis for robotic rehabilitation

An ankle-foot orthosis (AFO) is commonly used to help subjects with weakness of ankle dorsiflexor muscles due to peripheral or central nervous system disorders. Both these disorders are due to the weakness of the tibialis anterior muscle which results in lack of dorsiflexion assist moment. The deformity and muscle weakness of one joint in the lower extremity influences the stability of the adjacent joints, thereby requiring compensatory adaptations. We present an innovative ankle-foot orthosis (AFO) that was designed to allow two degree-of-freedom motion while serving to maintain proper foot position for subjects. The prototype AFO would introduce greater functionality over currently marketed devices by means of its inversion-eversion degree-of-freedom in addition to flexion/extension. The flexion/extension is controlled with the help of an actuator and inversion/eversion with a spring and a damper.

Gait training after stroke: a pilot study combining a gravity-balanced orthosis, functional electrical stimulation, and visual feedback.

Rationale: This case report describes the application of a novel gait retraining approach to an individual with poststroke hemiparesis. The rehabilitation protocol combined a specially designed leg orthosis (the gravity-balanced orthosis), treadmill walking, and functional electrical stimulation to the ankle muscles with the application of motor learning principles. Case: The participant was a 58-year-old man who had a stroke more than three years before the intervention. He underwent gait retraining over a period of five weeks for a total of 15 sessions during which the gravity compensation provided by the gravity-balanced orthosis and visual feedback about walking performance was gradually reduced. Outcomes: At the end of five weeks, he decreased the time required to complete the Timed Up and Go test; his gait speed increased during overground walking; gait was more symmetrical; stride length, hip and knee joint excursions on the affected side increased. Except for gait symmetry, all other improvements were maintained one month post-intervention. Conclusions: This case report describes possible advantages of judiciously combining different treatment techniques in improving the gait of chronic stroke survivors. Further studies are planned to evaluate the effectiveness of different components of this training in both the subacute and chronic stages of stroke recovery.

A gravity balancing leg orthosis for robotic rehabilitation

A number of methods can be found in the literature to gravity balance a machine. In this paper we use hybrid method to achieve gravity balancing. Hybrid method employs a mechanism to locate center of mass of the robot in conjunction with springs. This method is used to develop a rehabilitation device, which compensates the effect of gravity on a human leg. For a quantitative evaluation of the performance of the device, electromyograph data of the muscles involved in the motion of leg were collected and analyzed. This data showed that the machine could be used for gravity balancing of the leg and could be potentially used for rehabilitation of patients.

Design of a Novel Two Degree-of-Freedom Ankle-Foot Orthosis

An ankle-foot orthosis (AFO) is commonly used to help subjects with weakness of ankle dorsiflexor muscles due to peripheral or central nervous system disorders. Both these disorders are due to the weakness of the tibialis anterior muscle, which results in the lack of dorsiflexion assist moment. The deformity and muscle, weakness of one joint in the lower extremity influences the stability of the adjacent joints, thereby requiring compensatory adaptations. We present an innovative ankle-foot orthosis (AFO). The prototype AFO would introduce greater functionality over currently marketed devices by means of its pronation-supination degree of freedom in addition to flexion/extension. This orthosis can be used to measure joint forces and moments applied by the human at both joints. In the future, by incorporation of actuators in the device, it will be used as a training device to restore a normal walking pattern.

Exoskeletons for Gait Assistance and Training of the Motor-Impaired

Robotics is emerging as a promising tool for training of human functional movement. The current research in this area is focused primarily on upper extremity movements. This paper describes novel designs of three lower extremity exoskeletons, intended for gait assistance and training of motor-impaired patients. The design of each of these exoskeletons is novel and different. Force and position sensors on the exoskeleton provide feedback to the user during training. The exoskeletons have undergone limited tests on healthy and stroke survivors to assess their potential for treadmill walking. GBO is a gravity balancing un-motorized orthosis which can alter the gravity acting at the hip and knee joints during swing. ALEX is an actively driven leg exoskeleton which can modulate the foot trajectory using motors at the joints. SUE is a bilateral swing-assist un-motorized exoskeleton to propel the leg during gait.