| Based on the superior performance of ostrich toes travelling on sandy environment,we studied the phalangeal joint kinematics of ostrich toes on solid surface and loose sand surface,motion mechanism of self-adaptive travelling on sand,dynamics simulation travelling on sand of ostrich toes multi-posture.According to the principle of bionic and engineering bionic technology,four multi-posture casters bionic walking wheel were designed and tested by the trafficability on sandy environment.This paper provided a new research method and ideas of travelling in sand walking wheel casters,namely making walking wheel have active travelling sand function through changing caster postures.Firstly,we explored the phalangeal joint kinematics of ostrich foot on solid surface by constructing outfield experimental ground,high-speed camera and three-dimensional motion tracking analysis system Simi Motion software.Results showed that on solid surface stride duration and stance duration in running were shorter than that in walking,while dramatically increased their stride lengths.There was no significant difference was found in swing duration between walking and running.The MTP3 and MTP4 joints exhibited the largest range of motion whereas the first phalangeal joint of the 4th toe showed the largest motion variability.The interphalangeal joints of the 3rd and 4th toes presented very similar motion patterns over stance phases of slow walking and running.However,the motion patterns of the MTP3 and MTP4 joints and the vertical displacement of the metatarsophalangeal joint were significantly different during running and slow walking.the motions of the MTP3 and MTP4 joints are highly synchronized from slow to fast locomotion.This strongly suggests that the 3rd and 4th toes really work as an “integrated system” with the 3rd toe as the main load bearing element whilst the 4th toe as the complementary load sharing element with a primary role to ensure the lateral stability of the permanently elevated metatarsophalangeal joint.Gait parameters on loose sand surface were consistent with that on solid surface.The interphalangeal joint angles(?(11)?(11)?)of the 3rd and 4th toes presented very similar motion patterns over stance phases of slow walking and running.Gait had no significantly effect on the four key indicators of interphalangeal joint angles(?(11)?(11)?(11)?(11)?(11)?)at touch-down,mid-stance,lift-off and also the ranges of motion.The vertical displacement z of the metatarsophalangeal joint were significantly different during running and slow walking.At mid-stance,in running the metatarsophalangeal joint was closer to ground than that in slow walking,and the height were 7.0 cm and 11.1 cm,respectively.Motion gait had no significantly effect on the range ofmotion of the metatarsophalangeal joint displacements on x and y directions,which suggested that the metatarsophalangeal joint may effectively prevent the excessive movement and play an important role in protecting the ostrich toes.Motion gait had significantly effect on the range of motion of the toenail on y direction and the displacements were 3.6 cm and 5.2 cm,respectively.This further suggested that toenail may play a key role in doing an anchor on loose sand surface in locomotion.To further study travelling on sand mechanism of ostrich toe posture,we conducted dynamics simulation about ostrich toe posture in slow walking and running gaits travelling on sand.Simulation results showed that in running velocity field and force field of sand particle under ostrich foot were more intensive than that in slow walking.In walking ostrich foot had an obvious disturbance on the sand surface.However,sand particle thickness had no significant effect on sand disturbance phenomenon in running.From touch-down to 50% of stance phase,in running average contact force between the ostrich foot and sand particles was greater than that in walking,and the maximum of average contact force was about 7.5 × 10-3 N.From touch-down to 40% of stance phase,in running lateral force and vertical force acted on toe plantar were greater than that in walking,which showed that 25% posture and 50% posture played an important role in anti-slip and subsidence prevention.At the early stance period,in slow walking and running the force distribution of toe plantar was uniform.From mid-stance to lift-off,in running the force acting on toe tip and two sides of toe back were more intensive than that in walking,which further explained that toe papillae and toe back squama prevented ostrich toes from abrasive wear of sand particle.Based on ostrich toe phalangeal posture travelling on sand,we designed and processed four bionic walking wheel,namely herring-bone form wheel,one form wheel,V form wheel and combination wheel four bionic walking wheels and ordinary wheel.The tractive trafficability performance on sand of bionic walking wheels were tested using wheel-soil bin testing system.Results showed that when the wheel load were 10 N and the slip ratio was in the range of 17~33%,sandy traction trafficability of ordinary wheel was better than others.When the wheel load were 20 N and 30 N and the slip ratio was in the range of 17~23%,the drawbar pull force and traction efficiency corresponding to herring-bone form wheel were the maximal and rut was the shape of “W” pattern,and traction trafficability of herring-bone form wheel was superior to other wheels.When the wheel load was 50 N and 70 N and the slip ratio was greater than 35%,the drawbar pull force and traction efficiency corresponding to one form wheel were the maximal and rut was the shape of “double crescent”,and sandy traction trafficability of one form wheel was better than others.Therefore,on sand surface the traction efficiency of herring-bone form wheel was superior under the condition of wheel load was lower than 30 N and the slip ratio was lower than 35%,while one form wheel was superior under the conditionof wheel load was higher than 30 N and the slip ratio was greater than 35%. |
