Control of a regenerative braking powered ankle foot orthosis

Wearable robotic systems can be used to assist people suffering paralysis from stroke. This paper presents the mechanical design, electronics and control structure of a Powered Ankle Foot Orthosis for stroke survivors walking on a treadmill. The mechanical structure consists of a powered orthosis using a robotic tendon that uses a motor to correctly position a tuned spring in the gait pattern. During the gait cycle, the robotic tendon regenerates spring energy and uses that energy in order to assist the subject in push off and follow through into the swing phase of gait. Rather than using a motor and gearbox having several times the weight of the foot, which can supply the required peak power, a reduced energy robotic device is built with a 0.95 kg actuator that uses one third of the power and one half of the energy required by a standard motor/gearbox solution. This device controls the equilibrium position of the spring using a closed loop position controller. A real time embedded system was developed in the Matlab Simulink environment to form hardware in the loop simulations and allow rapid control prototyping. Not only direct-control is demonstrated using a predefined gait pattern but also State Logic is developed in order to determine the user's desired gait pattern. Experimental data, gathered from able body subjects walking on a treadmill prove that the system can assist gait by decreasing the peak power that a subject should supply by 50%. It is also demonstrated that springs can apply regenerative braking and that the concept is feasible and applicable in developing lightweight, functional wearable robots.