Study And Implementation On Hybrid Control Strategy Of Human-powered Augmentation Lower Exoskeleton

As a wearable robot,the lower limb assistive exoskeleton robot has a wide application prospects in military applications,industrial transportation,disaster relief,outdoor activities,medical rehabilitation and so on.The traditional control method is difficult to achieve better control effects in different gait phase or scene,and the hybrid control strategy which combines the advantages of multiple control methods have a better performance in actual system.This paper presents a hybrid control strategy based on a load-carrying lower limb assistive exoskeleton,which aims to shadow the pilot's movements quickly in different scenes,at the same time provides a certain amount of power assistance at the appropriate time to enhance mobility and reduce the muscle fatigue.The primary job of this dissertation can be summarized as follows:On the basis of human gait cycle and energy consumption analysis,the parameters of the anthropomorphic mechanical structure and hydraulic power system for HUALEX system are choosed.Due to the same action sequence is repeated in both left and right legs during walking,we only consider one leg in modeling and control,simplified humanmachine system models are established in both support phase and swing phase.A CoP-based gait detection method is proposed.It is a common human-machine interaction method to identify the intention of the pilot through the sole pressure information.We divide the human gait cycle into four stages: swing,heel-strike,stance and heel-off.The traditional gait detection method is based on the sole pressure threshold which vary with the different pilot,while the CoP-based gait detection methond can adapt to the change of the pilot's weight and provide more accurate detection results.Based on the gait pahse detection method,a hybrid control strategy for HUALEX system is proposed,which is composed of active control in support phase and passive control in swing phase,which can meet the different requirements of high torque and low bandwidth in the support phase and high bandwidth and low torque in the swing phase,and achieve better power assistance and wearing experience.Passive control is achived by changing the oil path through controlling hydraulic valve while active control is realized via using model predictive control to support the load,and the gravity compensation at heel-strike stage and the variable damping control at heel-off stage are used for smooth transition,preventing system instability and bad experience due to the sudden changes of torque.A hydraulic lower limb assistive exoskeleton robot system is built,which is comprised of Semi-anthropomorphic mechanical structure,hydraulic power unit,sensing and control system.The mechanical structure is mainly responsible for transmitting the back load to the ground,and the hydraulic power unit provides the power source for the exoskeleton joint,while the sensing and control system mainly obtains the status information of the human-machine system by sensors and controls the end effector to give power assistance at the right time to share the load with the pilot.The system performance test shows that HUALEX can carry up to 50 kg payload and walk at the speed of 5km/h.HUALEX system with the CoP-based gait pahse detection method and the hydrid control strategy can detecte pilot's movment intention quickly and accurately,and achieve walking,up and down slopes,up and down stairs under load.