A novel lower extremity exoskeleton (LEE) for assistive and rehabilitation applications

A large proportion of the global population suffer from impairments such as muscle spasms, partial or complete palsy and lack of aid in their lower limbs. As a result, some kind of technology is required that can assist paralysed patients with their day-to-day tasks, aid in neuro-rehabilitation and enhance the agility of its user, simultaneously. One such anthropomorphic robotic device is an exoskeleton. The objective of the present work is the mechanical design and development of a lower extremity exoskeleton (LEE) for assisting paralysed patients with their everyday routine and improving their quality of life, as well as for rehabilitation purposes. The designed joints of LEE have similar kinematics as that of human joints. LEE has a total of 10 DOF at both of its limbs: both active hip flexion/extension (Fl/Ext) and adduction/abduction (Add/Abd), active knee Fl/Ext, active ankle dorsiflexion/plantarflexion (DFl/PFl) and passive inversion/eversion (Inv/Ev) achieved with two parallel helical springs. The knee joint of LEE is designed to be a polycentric joint so that it can mimic the moving centrode of anatomical knee. For this, a double 4-bar mechanism (4-BM) is designed: trajectory tracing 4-BM and transmission 4-BM. Finally, finite element analysis of the thigh-hip connector link, thigh segment and shank segment of LEE is performed in ANSYS 2014, with Alloy Steel 4340, Aluminium Alloy 7075-T6 and Titanium-6Al-4V for testing its effectiveness to withstand the loads acting on it at static conditions without any significant deformations. Aluminium Alloy 7075-T6 is selected because of its lightweight, good corrosion resistance properties, high yield strength and low cost as compared to others. Future work on this paper will focus on enhancing LEE's mechanical framework to make it lighter, developing a compliant actuator system for improved human-machine coordination, a control framework for LEE and a self-balancing algorithm that will allow LEE to balance without the need for crutches.