Trajectory Tracking Impedance Controller in 6-DoF Lower-Limb Exoskeleton for Over-Ground Walking Training: Preliminary Results

Rehabilitation strategies based on robotic systems, like lower-limb exoskeletons, is expected to reduce the burden of locomotor impairment in patients with neurological diseases. In this work, we present the preliminary results of a trajectory tracking impedance control method applied to the Ex-oRoboWalker, a six degree-of-freedom (DoF) exoskeleton. The wearable robot was developed as an over-ground gait trainer to aid children and young adults with Cerebral Palsy (CP) achieve physiological gait patterns. The experiments were carried out in three healthy adults walking over-ground with the system working in three different modes: First, with the exoskeleton's motors unpowered, to assess the system's backdrivability, userrobot interaction and subject gait pattern; second, with the exoskeleton working in transparent mode; and finally, with the system working with the proposed impedance controller. As expected, when the exoskeleton is unpowered, the system presents low backdrivability, thereby resulting in high userrobot interaction torques and a nonphysiological gait pattern. However, the results show that the system was able to partially restore the subjects gait pattern and reduce the user-robot interaction torque when set in transparent mode. Finally, while working with the trajectory tracking impedance controller, the ExoRoboWalker was able to guide the subject through a target trajectory. This is the first step towards use the system as an over-ground gait trainer in CP population.

Automated summary

Robotic rehabilitation strategies, such as using the Ex-oRoboWalker with trajectory tracking impedance control, have shown potential in partially restoring subjects' gait patterns and reducing user-robot interaction torques.