Research On Biodynamics Of Human Lower Limb Based On Elastic Joint Drive

Exoskeletons are mainly divided into active and passive types.Active exoskeletons have inherent defects in structure,e.g.price,energy and response speed.Passive exoskeletons avoid these defects and gradually become a hotspot in exoskeleton research;however,they have the disadvantages of low energy recovery and low energy conversion efficiency.In this paper,to further optimize the passive exoskeleton,the principle of storing gravitational potential energy and kinetic energy and controlling the energy with multi-stage locking mechanism was proposed.The multi-level energy locking mechanism can adapt to different body weights and walking speeds and can control its own opening and closing through specific motion signals to achieve efficient energy recovery and release.Firstly,an exoskeleton structure model was designed based on the proposed principle of exoskeleton assistance,including hip,knee,ankle joints,and multi-level energy locking mechanism,transmission system and framed system.The wearing comfort test of the exoskeleton was completed.Then,the first-generation mechanical model of exoskeleton was built.The mathematical model of human-machine coupled motion and human motion in the energy release phase and energy storage phase were established respectively,in that case the hip torque curve was obtained.At the same time,based on the ADAMS software,a dynamic simulation model with the same motion state was established and the hip torque was simulated.The torque curves of the hip joints in the energy release phase of the two models have a high degree of correlation and coincidence;however,due to the impact,the torque correlation of hip joint in the energy storage stage was low.The result shows that the foot reaction of the simulation model and experiment has a high degree of coincidence,which verifies the correctness of the simulation model.Compared with the torque curve of the hip joint with and without the exoskeleton,and the work value of the hip joint was reduced by 9.61%.Finally,the ADAMS simulation model was used to optimize the dynamic performance of the first exoskeleton machine with the hip joint length and spring stiffness as variables.The results indicated that the hip joint work value was reduced by 33.44% compared with the non-wearing.Furthermore,the exoskeleton was redesigned and an exoskeleton optimization machine was produced to provide conditions for the assisted performance experiments.The multi-level energy locking mechanism was studied.Firstly,the ADAMS dynamic model was used to simulate the action mechanism of the multi-level energy locking mechanism.The results demonstrated that the multi-level energy locking mechanism increased the energy storage efficiency of the exoskeleton by 236.11%.Then,the adaptability of the multi-level energy locking mechanism to different weights and different speeds was explored.The results showed that the multi-level energy locking mechanism could satisfy the adaptation to different weights and speeds.Finally,the energy conversion laws of different body weights and velocities in the energy storage stage were researched,and the energy change model of the lower limbs in the energy storage stage was established.The calculation results showed that the exoskeleton could store almost all the kinetic energy and gravitational potential energy lost during the movement of the lower limbs.Biomechanical experiments were carried out using the exoskeleton optimization machine.The sEMG changes of the muscles that mainly contributed to walking were measured.Compared with the sEMG scores of walking with or without exoskeleton assistance,the experiment proved that the total sEMG score was reduced by 9.12% after wearing the exoskeleton.At the same time,the Physiological Cost Index(PCI)was used to comprehensively evaluate the movement consumption of human body wearing exoskeleton.The paired-samples ‘t test' was used to evaluate the significance of the results of wearing and not wearing exoskeleton experiments.The results showed that there was no significant difference in PCI between the two groups for short distance sports of 60 m and below,but significant change in PCI during walking at normal speed of 6min and above,with a reduction of 17.07%.