Development of a Lower-Limb Active Orthosis and a Walker for Gait Assistance

Abstract

Lower-limb exoskeletons and powered orthoses in gait assistance applications for patients with locomotive disorders possess the potential to significantly affect society in the near future. This paper presents the primary features of a lower-limb exoskeleton to enable paralysed children to walk. Because these patients are unable to move their limbs, the device generates their basic motions in everyday life, e.g., standing up, sitting down, and stable ambulation. A walker provides stability in the lateral plane, while the active orthosis provides stability in the sagittal plane while walking. The walker has been devised with a two degree of freedom mechanism to allow the user to sit down and stand up in a stable and comfortable way without the movement of the walker itself. The gait of the orthosis parameters such as step height, body height or step length are modified online, based on an impedance control approach, providing a safe and smooth gait pattern. Two shoe insole pressure measurement systems provide ground reaction force and center of pressure to adapt these gait parameters online. An adjustable compliance actuator has been designed and incorporated to the knee joint of the active orthosis. This Actuator with Adjustable Rigidity and Embedded Sensor (ARES) fulfills the demanding characteristics required in an active orthosis’s joint, namely, intrinsic compliance to allow human-machine interaction, high power-to-weight ratio, high peak torque, small size and low weight. Exploiting the characteristics of ARES actuator a control scheme has been designed and implemented to achieved a reduction in the energy expenditure while keeping compliant to accommodate unexpected disturbances. The final ATLAS exoskeleton has been successfully tested in a healthy user, in a quadriplegic child, and in a patient with neuromuscular disease.