Interlimb Parallel-Link Powered Orthosis (IPPO): Compact Wearable Robot With Lateral Weight Bearing Mechanisms for Gait Assistance

Most wearable robots require the additional use of a walking aid for maintenance of balance and bearing the body weight. Although joint degrees of freedom (DOF) in the frontal plane are important for lateral balance, the number of active joint DOFs is also responsible for increase in robot size and weight. The Interlimb Parallel-link Powered Orthosis (IPPO), a newly developed wearable robot with a compact drive mechanism based on the medial system, forms the subject of this paper. IPPO has 9 active DOFs including a mechanism allowing the simultaneous movement of the stance hip adduction and swing hip abduction using one actuator. Two experiments were conducted for a preliminary proof-of-concept study wherein the standing posture center of pressure was evaluated amidst the lateral sway induced by IPPO. We confirmed that our prototype could assist the lateral movement of the user's body center of mass. In the performance experiment of walking on a treadmill, the results showed that the arm loading forces and arm muscle activities were reduced when the lateral weight bearing was assisted by IPPO. We conclude that the lateral weight bearing mechanism is feasible and effective for reducing arm loading by assisting the lateral weight bearing during walking.