Robust nonlinear control of an intrinsically compliant robotic gait training orthosis

Robot-assisted gait therapy is an emerging rehabilitation practice. This paper presents new experimental results with an intrinsically compliant robotic gait training orthosis and a trajectory tracking controller. The intrinsically compliant robotic orthosis has six degrees of freedom. Sagittal plane hip and knee joints were powered by the actuation of pneumatic muscle actuators in opposing pair configuration. The orthosis has passive hip abduction/adduction joint and passive mechanisms to allow vertical and lateral translations of the trunk. A passive foot lifter having a spring mechanism was used to ensure sufficient dorsiflexion during swing phase. A trajectory tracking controller based on a chattering-free robust variable structure control law was implemented in joint space to guide the subject's limbs on physiological gait trajectories. The performance of the robotic orthosis was evaluated during two gait training modes, namely, "trajectory tracking mode with maximum compliance" and "trajectory tracking mode with minimum compliance." The experimental evaluations were carried out with ten neurologically intact subjects. The results show that the robotic orthosis is able to perform the gait training task during the two gait training modes. All the subjects tend to deviate from the reference joint angle trajectories with an increase in robotic compliance as the subjects have more freedom to voluntarily drive the robotic orthosis.