Bounded control of a full-exoskeleton device with four (4) Degree of Freedom

This study deals with the bounded control of a lower limb exoskeleton having four (4) Degree of Freedom (DoF), which are located at hips and knees joint level. It is intended to be used as a rehabilitative device for individuals with hip or knee joint impairments. The rehabilitation protocol entails using Central Pattern Generators (CPGs) to design rhythmic movement close to that of the human gait. In order to remedy the drawback associated with CPGs which is characterised by the inability to choose specified initial conditions for the generated trajectories, the use of time polynomial functions is employed to approximate the joint angle profile generated. This gait is meant to be tracked by the user under the influence of a controller. The control torque is envisaged to ensure a proper trajectory following of the exoskeleton for the flexion/extension movements of the hip and knee within the range of motion associated with walking. With this approach, the wearer is completely passive. Using a bounded controller further protect the user and the device by ensuring the actuator´s physical limits are not exceeded. Simulation results with the aid of Matlab/Simulink does help validate the proposed assertion.