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.