An Active Impedance Controller to Assist Gait in People with Neuromuscular Diseases: Implementation to the Hip Joint of the AUTONOMYO Exoskeleton

Medical and personal exoskeletons of the lower limbs have successfully been oriented toward persons with complete spinal cord injury (SCI). Persons with less disabling disorders such as muscular dystrophy, multiple sclerosis, hemiplegia or incomplete paraplegia, however require more freedom of motion and greater possibilities for interaction with the device. An assistive strategy relying on a finite-state controller is addressed in the current paper and implemented about the hip flexion-extension during walking. The paper focuses on three major issues. The first one looks at the feasibility and effectiveness of using an active impedance controller with a non-elastic actuator, where typically a transmission ratio of approximately 1:200 allows a torque of about 40 Nm. Secondly, the detection of intention based on volitional motion recognition is evaluated regarding the limitations encountered by the targeted populations. Finally the appropriateness of the three states variable impedance controller is addressed with two pilots, one healthy and one with muscle weakness due to a limb girdle muscular dystrophy (LGMD). The AUTONOMYO exoskeleton used is a lower limb device consisting of three actuated degrees of freedom per leg about the hip (flexion and abduction) and the knee (flexion) while the ankle is semi-rigidly constrained. Results show that the implementation of impedance behaviors on a rigid transmission shows satisfactory performances while it necessitates some active compensation. The controller has been successfully and safely used by both pilots, demonstrating a promising usability to assist people with incomplete gait impairments.