Research On The Mechanical Performance Design Of An Innovative Lower Extremity Exoskeleton

The fulfillment of lower extremity exoskeletons requires the technologies of the mechanics, the robotics, the bionics, the control theory, the information processing, the communications, the sensors, the computations, and etc. The lower extremity exoskeleton combines the intelligence of the human and the power of the mechanism to complete tasks and implement functions. The thesis introduced the development history and the categories of the lower extremity exoskeletons, as well as the research status. In the thesis, we proposed an innovative hybrid lower extremity exoskeleton for power augmentation based on the theory of the type synthesis. The mechanical performance design of the exoskeleton is elaborated. The research results provide a theoretical basis for the design and research of the lower extremity exoskeletons for power augmentation. The main work of the dissertation can be concluded as:(1) The criteria for the mechanical design of the lower extremity exoskeletons are listed and an innovative lower extremity exoskeleton with hybrid structures for power augmentation is proposed. The layout of the articulations and the allocation of the degrees of freedom are elaborated according to the human physical structures. Anthropomorphic legs with parallel mechanisms are adopted, which have similar structures as the human hips and ankles but no knees. The active joints and the passive joints are determined according to the human walking dynamics. The structure of the parallel mechanism is optimized for good walking performance.(2) The states of the lower extremity exoskeleton are classified and described by specific meaningful notations in a systematic and concise manner. The kinematic characteristics of the end effectors in the different states are achieved and a new concept of Characteristic State is proposed to uniquely indicate the type of motion that the wearer is going through. The models of the configuration, the velocity and the force are elaborated based on different topologies.(3) The influences of the dimensions on the motion following ability and the load carrying ability are analyzed based on the kinematic model of the exoskeleton. The size optimizations of the parallel sides are performed for the parallelogram mechanism and the kite mechanism respectively. The joint ranges of the exoskeleton are determined within the joint ranges of the human in consideration of the safety and the workspace of the lower limb is calculated(4) Dynamic models including the interaction between the exoskeleton and the wearer are developed according to the different states of the lower limbs. Springs are introduced to the parallel mechanism to improve the load-carrying ability. A novel actuator called Hy-Mo is introduced to the lower extremity exoskeleton, which utilizes the hydraulics to provide powers and adopts the motor to achieve the position control. The actuator sizes and the actuator mounting points are selected according to the joint ranges and the required joint torques.(5) The pendulum model of the human lower limb is analyzed and the natural frequency is determined. The pendulum model of the exoskeleton lower limb is also analyzed and the relationship between the natural frequency and the masses is established, which can be used to design the dynamical parameters of the exoskeleton. The swing motion of the lower limb of the exoskeleton at different frequencies, including the resonant frequency is realized in experiments.(6) The center of percussion of the human lower limb is determined. The relationship between the center of percussion of the exoskeleton and the masses is established, which can be used to decide the location of the center of percussion so that the hip of the exoskeleton will not suffer great forces when the leg is under a shock. The actual position of the center of percussion of the exoskeleton lower limb is decided by experiments.