Affiliations: State Key Laboratory of Robotics and System, Harbin Institute of Technology, Harbin, Heilongjiang, China
Correspondence:
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Corresponding author: Yanhe Zhu, State Key Laboratory of Robotics and System, Harbin Institute of Technology, C1-203, HIT Science Park, 2 Yikuang Street, Nangang District, Harbin 150080, Heilongjiang, China. E-mail:yhzhu@hit.edu.com
Abstract: Unlike traditional rigid actuators, the significant
features of Series Elastic Actuator (SEA) are stable torque control, lower
output impedance, impact resistance and energy storage. Recently, SEA has
been applied in many exoskeletons. In such applications, a key issue is how
to realize the human-exoskeleton movement coordination. In this paper,
double closed-loop cascade control for lower limb exoskeleton with SEA is
proposed. This control method consists of inner SEA torque loop and outer
contact force loop. Utilizing the SEA torque control with a motor velocity
loop, actuation performances of SEA are analyzed. An integrated exoskeleton
control system is designed, in which joint angles are calculated by internal
encoders and resolvers and contact forces are gathered by external pressure
sensors. The double closed-loop cascade control model is established based
on the feedback signals of internal and external sensor. Movement
experiments are accomplished in our prototype of lower limb exoskeleton.
Preliminary results indicate the exoskeleton movements with pilot can be
realized stably by utilizing this double closed-loop cascade control method.
Feasibility of the SEA in our exoskeleton robot and effectiveness of the
control method are verified.
Keywords: Exoskeleton, Series Elastic Actuator (SEA), torque control, cascade control
