Adaptive Stair-Ascending and Stair-Descending Strategies for Powered Lower Limb Exoskeleton

Enhancing the life quality for patients with spinal cord injuries (SCIs) by means of improving their mobility in daily life assisted by powered lower exoskeletons is practicable and significant. Being a part of typical daily activities, stairs with different sizes are supposed to be a usage scenario of exoskeletons aiming for extending patients' sphere of activities. This paper proposes strategies for automatically ascending/descending stairs with different sizes within the national standard based on the powered lower limb exoskeleton AIDER. The developed strategies employ infrared range sensors, foot pressure sensors and angle encoders to identify stairs whose sizes are computed based on kinematics. In addition, a methodology named "Stick From the Origin" aiming at recognizing stairs more accurately is proposed during the stair-ascending process. The Zero Moment Point (ZMP) stability criterion based on the foot pressures is utilized to ensure safety in the entire process. Experiments have been undertaken to testify the practicability and universality of the proposed strategies, by applying which AIDER can assist patients with various physiological characters to accomplish stair-climbing tasks.