| The lower extremity exoskeleton for power augmentation with series-parallel mechanism is a wearable robot on the operator’s legs, which can match the degrees of freedom and the motion ranges of human being’s legs. And it can walk on tough terrains, greatly enhancing the operator’s power and endurance, which is mainly used in the urgent situations, which people have to carry heavy mission-critical equipment, such as medical rescuing, earthquake relief, soldier carrying weapons and worker moving heavy things. The characteristics and application background of lower extremity exoskeleton robot put forward basic theory and technology challenges from all the respects, which include the biomimetic design, motion following performance of the mechanism, joint driving torque and power under various kinds of humanoid gaits and control algorithms facing the complex inputs and high nonlinear exoskeleton system. The biomimetic design should satisfy the basic requirements of motion ranges of human legs while not hurt the body. High motion following performance of the mechanism can guarantee the comfortability and safety of the operator’s body. This article proposed a lower extremity exoskeleton with a topology of series-parallel mechanism. And based on the exoskeleton, we analyzed the motion following performance, proposed various motion following performance indexes, established the kinetic model of the exoskeleton to analyze the gait dynamics and proposed an intelligent control algorithm for walking. The structure is as follows:(1) We proposed a novel lower extremity exoskeleton and each single leg has 6 DOFs. The joint angle variation during the gait of human beings was simulated and analyzed. The human leg mechanism model was established for simplification. According to the distribution of degrees of freedom of human legs and the motion ranges of each joints, we proposed a 12-DOFs lower extremity exoskeleton with a topology of series-parallel mechanism. The working model of the exoskeleton-human system was analyzed and the force transmission characteristics were revealed. The characteristics of the stabilization of the exoskeleton and human system were analyzed.(2)The motion following performance concept and indexes of the lower extremity exoskeleton were proposed. According to these indexes, the motion following performance model was established to compare the end-effector in x, y and z directions thoroughly and experiments were done to verify the model. To judge the extent of the error sources’ effects on the motion following performance, we conducted the sensitivity analysis and obtained the anti-interference ability of the end-effector. Finally, the suggestions for improving the motion following performance were given.(3) The extent of the speed, load and ground gradient’ effects on the driving torque and power were illustrated. The mapping between the human lower limb and the lower extremity exoskeleton was established. The dynamic model of the exoskeleton was conducted for analyzing the humanoid gaits. The driving torque and power of each joint during the gait cycles were computed and the extent of the speed, load and ground gradient’ effects on the driving torque and power were analyzed, which provides the basis of the driving system design and control laws.(4) A new switch-type fuzzy-PID/PID controller was designed and based on the controller co-simulations of the exoskeletons on various gaits were analyzed. This controller can handle with the high nonlinear system of the exoskeleton, imprecise dynamic model and the complex inputs from the outside, which can choose the better algorithm. When choosing the fuzzy algorithm, the controller can adjust its parameters and rules. Co-simulations of level walking, stair ascent and descent, squatting down and standing up and side kick were done based on the proposed controller. The effectiveness and feasibility were verified from the simulation results. At last, the stabilization and optimal control were analyzed.
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