Active control strategy of lower limb exoskeleton based on variable admittance control

Lower limb exoskeleton is a typical wearable robot to assist human motion with physiological power improvement. The active mode experiments based on the constant admittance parameters are carried out to acquire the original data. Then the fast fourier transform(FFT) together with linear fitting methods are used to process the original data and to obtain the optimal admittance parameters with different step frequencies. A variable admittance controller is adopted to implement the active follow-up control of exoskeleton to deal with the time-varying step frequency, which means that the operator's motion is motivated by his/her intention. Meanwhile, the exoskeleton control tries best to improve the wearable comfortable performance of human–exoskeleton system. The effectiveness of the proposed control scheme is verified by both the comparative simulations and experimental results of the human–exoskeleton cooperative motion.