Leg-foot Bionic Design Of Quadruped Delivery System Based On Blue Sheep's Stable Mountaineering Characteristics

Land vehicle systems,as indispensable means of transport for the daily life and work of mankind,play a vital role in the fields of transportation,exploration,defense,disaster relief and planetary exploration.However,conventional vehicle systems that work on steep slope and complex road,such as mountain forests and disaster sites,cannot pass smoothly.The development of leg-foot vehicle system and robot provides a strong guarantee for the vehicle system to walk steadily on irregular road,and the quadruped vehicle system is one of the main systems.The quadruped vehicle system mainly imitates the limb structure and movement pattern of animal in nature.None of the current existing quadruped vehicle system has the ability to crawl stably on slopes above 30°,and cannot walk on steep mountains,so there is an urgent need to develop a quadruped vehicle system with superior climbing performance.The other bionic prototypes have no superior climbing performance.By contrast the blue sheep living in the Himalayas have superior climbing properties compared with other tetrapod and can walk freely on cliffs,providing an excellent bionic model for the development of a quadruped vehicle system with superior climbing properties.Therefore,this study employs blue sheep as bionic prototype to analyze the climbing mechanism of blue sheep by analyzing the bone structure characteristics,kinematic characteristics and kinetics characteristics of blue sheep.The passive contact stability of hoof was proposed based on the material,structure and mechanical propery analysis.Based on this,bionic anti-slip foot and bionic leg-foot system were designed and manufactured.The anti-slip performance of bionic anti-slip foot and the anti-slip performance of bionic foot system were then tested,and the foot parameters of bionic foot system were optimized.The main research contents and conclusions are as follows:1)Research on the gait characteristics and joint angle motion characteristics of blue sheep during climbing on different slopes.Kinematics data is acquired through the three-dimensional motion capture system,and the kinematic characteristics of blue sheep walking on different slopes are analyzed.The results show that the longest gait period of the blue sheep when walking on flat ground.At a small slope of 5°?15°,the gait cycle increases with the increase of slope degrees,on a large slope of 20°?35°,the gait cycle shows a decreasing trend as the slope degrees increase.At the same time,the step length decreases as the slope degrees increase.On a slope of 5°?15°,the velocity decreases with the increase of the slope degrees,and it jumps to 0.33 m/s on the slope of 20°,and then gradually decreases with the increase of the slope degrees.Blue sheep gait symmetry gradually decreases with the increase of the slope degrees.In addition to 35 degrees on the forelimb elbow and wrist joints,the variation trend of the angle from leaving to re-touching the ground is consistent in the other slopes.The variation trend of the hindlimb knee and ankle joints angle from leaving to re-touching the ground is consistent in the all slopes.And the variation of the wrist,knuckle,ankle,and toe joints angle are unaffected by the change in slope degrees.2)Research on the Vertical ground reaction force of blue sheep during climbing on different slopes.The vertical ground reaction force of blue sheep during climbing on different slopes is obtained by using pressure plate system.This study analyzes the difference between the front and rear hooves and the symmetrical between the left and right hooves of the vertical ground reaction.This research divides the hooves of blue sheep into four quadrants,and the distribution and transform rules of the vertical ground reaction force in four quadrants are also obtained.The results show that when walking on flat ground,the PVF and VI symmetry index on the left and right sides of the front and rear hooves of the blue sheep are all above 99%.As the slope degrees increase,the symmetry index decreases.When walking on flat ground,the fore limbs of the blue sheep bear greater PVF and VI.As the slope degrees increases,the proportion of the PVF of forelimbs decreases.The vertical force on each slope is transferred from the lateral caudal quadrant to the medial cranial quadrant.As the slope degree increases,the main stress quadrant of the front hooves is transferred from the intra-tail quadrant to the intracranial quadrant.The main force quadrant of the rear hooves is the intracranial quadrant and does not change with the slope degrees.3)Research on the passive contact stability mechanism of blue sheep's hoof during climbing on slopes.Using a combination technology of scanning electron microscopy,infrared spectroscopy,and nano-indentation to characterize the surface morphology,structure,material composition,and mechanical properties of the blue sheep hooves,and study their contributions to passive contact stability.Finally,the effect of surface morphology and microstructure on anti-skid and buffering impact is analyzed by finite element method.The results show that there are three kind of micro-morphology on the surface,including straight layer unit,back-shaped sheet layer and vertical stripe.The micro-morphology can increase the friction between blue sheep's hooves and the ground or rock,and play an anti-skid role in blue sheep's mountaineering.The corneum of blue sheep's hooves is mainly composed of keratin,the outermost layer is highly mineralized,and it can improve the fracture toughness and mechanical rigidity.There are four layers of coupling structure hard-soft-hard-soft which can improve the mechanical performance of the blue sheep hooves and resist the impact of blue sheep hooves colliding with rocks.4)Based on the analysis of the biological characteristics of blue sheep's hooves,bionic anti-slip feet are designed.Then kinematics modeling is built.The position and posture of the bionic hoof at a given joint angle are obtained based on positive kinematics analysis.Through negative kinematics,the joint angle of each joint at a given hoof position and posture is obtained.Finally,the accuracy of kinematics model is verified by MATLAB.5)Based on the musculoskeletal structure of the blue sheep's hindlimbs,the bionic leg-foot system is designed and fabrication.The bionic foot anti-slip performance test platform is also established.The hardness of flexible hoof sole and elastic coefficient of simulated ligament of bionic non-slip hoof were designed and optimized,to obtain their regression equation with the anti-skid performance index.The effect of the hardness of flexible hoof sole and elastic coefficient of simulated ligament on the anti-skid performance is analyzed.The kinematics and motion control strategy of blue sheep during climbing on different slopes are investigated.The motion patterns of lower limbs and the distribution and transfer law of vertical reaction force were also obtained,which may provide valuable reference for the power output control of the vehicle system.The passive contact stability was proposed.And bionic leg-foot system was designed and fabrication.Then anti-sliding performance measurement of bionic leg-foot system was conducted.In final,the effect of the hardness of flexible hoof sole and elastic coefficient of simulated ligament on anti-sliding performance was discussed.The research may supply key biomechanical and design technical basis for the development of new quadruped vehicle system with superior climbing performance.