Anthropomorphic design and control of a polycentric knee exoskeleton for improved lower limb assistance

Around one billion people (15% of the global population) suffer from impairments such as muscular weakness, partial or complete paralysis, and lack of assistance in their lower extremities. As a result, robotic devices such as the exoskeleton are used to assist paralysed patients with their day-to-day tasks, aid in neuro-rehabilitation, and enhance the mobility of the user, simultaneously. In this paper, the design and control of a lower extremity exoskeleton with a polycentric knee joint, named as EXXON is presented. It is designed in a way such that it can provide assistance to paralytic patients for performing daily tasks and improve their quality of life and to aid faster and better rehabilitation. Based on the degrees of freedom (DOF) and range of motion of the human lower limb joints, the joints of EXXON has been designed. EXXON has a total 10 DOF at both of its limbs: both active hip flexion/extension and adduction/abduction, active knee flexion/extension, active ankle dorsiflexion/plantarflexion and passive inversion/eversion. The knee joint of EXXON 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 is designed. The first 4-bar is for tracing the trajectory of the anatomical knee while the second one is for transmitting the torque to the first 4-bar from the knee actuator. A dynamic model of EXXON has been developed for its controlling. A Computed Torque Controller is designed to simulate the dynamic model of EXXON, such that its joints can track the desired gait trajectories. Simulation results with the developed controller are also presented.