Study On Mechanism Of Falling Of Lower Extremity Exoskeleton Robot

As the aging of population aggravates and the number of people with disabilities in the lower extremities increases,the demand for medical devices in rehabilitation training and walking aids also gradually increases.The powered lower limb exoskeleton can help people who have lost part or all of their walking ability to walk upright and achieve the goal of rehabilitation training or walking assistance.The design and application of the exoskeleton system has become a hot topic of research.However,the safety issue when use exoskeletons has not been effectively solved,especially the risk of falling is still in the initial stage of research.The key issue such as how to improve the stability of man-machine system and assess the consequences of man-machine falls need to be resolved urgently.This paper analyzed the cause,process and result of human-machine fall through the principle of stability determination,man-machine fall test and finite element crash simulation,and obtained the characteristics of fall motion and assessed injury of human body.The main contents are summarized as follows:?1?Starting from the fall of the human body,the definition of human-machine fall was defined,and we also divided the types of fall and injury caused by fall.The process of exoskeleton using was decomposed into three stages of standing,walking and standing up.Based on the principle of zero moment point and supporting polygon,the reasons for the fall were analyzed.?2?A man-machine fall experiment platform was established and a fall simulation experiment carried out.A motion capture system including eight high-speed cameras was used to record the process of human with exoskeleton falling.The experiment included single human fall and man-machine system fall,in different direction which backward falling,sideward falling and forward falling.The software was used to model and reproduce the fall process,the change of the human posture during the fall was acquired,and the head velocity data was collected to parameterize the fall process.?3?Based on the finite element method,we simulated the man-machine system crash collision.By using 3D software to get modeling of exoskeleton,combined with the whole body standing model M50-PS,a 3D model of human wear with exoskeletons was constructed.The human-machine system was meshed by pre-processing software,the initial conditions of the fall were set according to the data obtained from the experiment,and the human body biomechanical response results were finally obtained.The results show that,without initial speed and any protective action,the head-to-ground collision speed reaches 6.5m?s^-1,which can cause traumatic brain injury.No fractures were found in other parts,but there were local scratches and squeezing.?4?Based on the characteristics of man-machine fall,we designed a fall-buffering posture.After the man-machine system adopts a buffer posture,the impact velocity of the hips to the ground when falling backwards is reduced from 4.7m?s^-1 to 3.0 m?s^-1,and the head can be prevented from impact.The knees hit the ground with velocity of 2.8m?s^-1when falling forwards,and that can also protect the head and reduce the risk of falls.The research work in this paper filled the gap in the evaluation of human wear with exoskeleton falling injury,and further promoted the research of exoskeletons in the safety issues.