Development of a Powered Assistive Device for Patients with Lower Limb Muscle Weakness

Abstract

Lower limb orthoses are wearable robotic devices used to assist people suffering from diseases such as paralysis, paraplegia, foot drop, muscle weakness, etc. People suffering from such diseases either lose their ability to walk or they walk in an asymmetric gait cycle with reduced speed and get exhausted easily by walking a short distance. The commercially available orthosis is very costly and moreover they do not provide complete rehabilitation. In the study, people suffering from lower limb muscle weakness are considered and a simulation study on orthosis design to assist them during swing phase of ground-level walking is described. The structural as well as functional aspect of a biological leg is considered to perform the simulation. Three-link (representing thigh, shank and foot) model is considered to perform the simulation of human lower limb in swing phase. Based on biomechanics, different muscles of lower limb are mimicked by using springs and series elastic actuator. A trajectory optimization problem is formulated to get human leg model’s hip, knee and ankle joint trajectories in the range of normal human during swing phase by varying stiffness of different springs and biarticular actuator parameters. The simulation results showed that the model’s different joint trajectories are well within the bounds of normal human by using only one biarticular series elastic actuator at the place of gastrocnemius muscle and passive elements such as springs. Thus, we can assist human during the swing phase of ground-level walking by using such a small actuator set.