State-Based Control for an Actuated Reciprocal Gait Orthosis

Upright locomotion has many health benefits for patients with spinal cord injury. Passive gait orthoses, such as an isocentric reciprocal gait orthosis (IRGO), allow patients to walk by pushing themselves forward with forearm supports. To move the legs, the IRGO physically couples the motion of stance and swing leg through a linkage. Unfortunately, this locomotion is associated with high metabolic effort. To reduce the metabolic demand while maintaining the advantages of simplicity and low weight of an IRGO, we propose the extension of an IRGO with a single actuator directly integrated into the rocking mechanism and investigate the use of a Hybrid Zero Dynamics based controller to support the user. This is a time-invariant feedback controller, in which a stable reciprocal gait is designed by means of numerically optimized virtual constraints. We evaluate the feasibility of this approach in a sagittal plane model of the dynamic system. For a range of walking speeds and step lengths, we are able to show that the chosen approach has the potential to safely support impaired users walking with IRGOs. The obtained gaits were periodic, stable, maintained a minimal ground clearance and could be implemented with a driving torque of 50 Nm.