Lower body exoskeleton-supported compliant bipedal walking for paraplegics: How to reduce upper body effort?

This paper introduces a position-based compliance control algorithm that can be implemented in a lower extremity exoskeleton-supported paraplegia walking task, in which upper body has to be utilized to maintain the overall balance. In order to reduce the upper body effort required during the task, the controller is designated to be capable of managing the position/force trade-off in conjunction with an active admittance regulator scheme. In the case of no force errors, the controller prioritizes position tracking in a way to achieve walking support. Once the force error increases (e.g., ground reaction force peaks, unexpected disturbances, stepping on an object, etc.) the position reference is updated in accordance with the force constraints and active admittance characteristics. By the virtue of this strategy, the human-robot system exhibits enhanced environmental interaction capabilities; therefore, the subject can maintain the overall balance with relatively less upper body effort while walking. Implementing the proposed method, we conducted robot-assisted walking experiments on 4 able-bodied subjects with different body mass index levels and genders. Subjects were instructed to be in passive mode. In addition, walking with severe obstacles was also experimented on a single able-bodied subject. In conclusion, the proposed method enabled us to yield enhanced walking performance comparing to classical rigid position control scheme; indicating that it could potentially introduce a compliant locomotion control alternative for the paraplegia walking support task with a comparatively less amount of upper body effort requirements.