Investigation of CVT-based Hybrid Mechanism for Torque Variations in a Knee Exoskeleton

Abstract

One of the major problems faced by elderly people is independent mobility. Till now, widely accepted conventional mobility solutions are crutches, wheelchairs, and walkers etc., which hardly give any independence and have other disadvantages also. To provide a better mobility solution, interest in wearable exoskeletons is increasing. It is important, to focus on the growing needs of the elderly people as assistive exoskeletons have the potential to play a major role in helping elderly persons to maintain independence and good quality of life. This thesis provides a crisp review of state-of-the-art in exoskeletons by providing a classification methodology, comparing their constructional features and also critically analysing the pros and cons of systems which have been realized. Regulatory issues, important for realizing new markets for the technologies, are also explored in this work. Main focus of the thesis is to explore new technologies to make the exoskeleton more cost effective so that it can be accessed by the masses. Torque variation methods of the exoskeletons are surveyed and a new cost effective solution is investigated by using Continuous Variable Transmission (CVT) and conventional mechanisms. The feasibility of a step-cone type CVT to provide torque variation for sit-to-stand motion at knee joint is investigated by using optimization methods in MATLAB environment. The torque range data for the optimization purpose is taken from the experimental results from our Swedish group. Optimized CVT is then coupled with a scotch yoke mechanism for motion reversal and four-bar chain for poly-centricity at the knee joint by developing a mathematical model. Then geometric modeling of the complete assembly is made and simulation is done in MATLAB/Simulink. For validation, the results are compared with walking gait cycle of the normal healthy human being. Future work will focus on finding more alternate cost effective methods and the experimental validation of the results by prototyping and testing on human subject.