Bionic Study On Vibration Reduction And Self-Adaption Walking-Wheel Foot Bases On The Structural Characteristics Of Ostrich Metatarsophalangeal Joints

Ostrich(Struthio camelus) is native to African desert and gebi region. It is capable of super-speed and remarkable endurance. The permanently elevated metatarsophalangeal(MTP) joint of ostrich foot plays an important role in storing energy and vibration reduction during high-speed movement. Based on reverse engineering, kinematics analysis, foot pressure measurement and other technological means, this paper studied the three-dimensional structure of MTP joint of ostrich foot and its mechanism of vibration reduction. Then, combined the result and bionic mechanism, a vibration reduction and self-adaption bionic walking-wheel foot was designed by the engineering bionics and finite element method.In order to confirming the relative position of internal tissues of ostrich foot and the mechanism for permanently elevated MTP joint, the MRI medical imaging method was utilized to obtain the medical image data of tissue structure of ostrich foot,and the three-dimension structures of bones, tendon and tendon sheath were reconstructed and those relative positions of the space were reappeared by the reverse engineering software of the Mimics and Geomagic studio. Then, several ostrich feet were dissected to study the accurate interrelation among tendons and tendon sheath.Finally, it was found out that the MTP joint was elevated by flexor tendons in ostrich foot and the connective tissue which connected distal tarsometatarsus and tendon sheath.The macro- and micro- structures of tendons were observed to study its effect on vibration reduction in different location of ostrich foot MTP joint. Macroscopically,the tendon fibers arranged linearly in the middle MTP joint, and the tendon fiber bundles showed a wave-like arrangement in both ends of the tendon of flexor perforans et perforatus digiti III and the tendon of flexor perforatus digiti III, while the regularity of arrangement was not obvious in the tendon of flexor digitorum longus. Microscopically, tendon collagen fibers were aligned with horizontal and vertical mode in the middle MTP joint, while the tendon collagen fibers were wavy shape in both ends of MTP joint. The shape of tendon fiber bundles and collagen fibers are closely related to the function of tendons. During ostrich foot contacting with the ground, the tendons in upper end of MTP joint can store energy by stretching fiber bundles and collagen fibers or release energy by rebounding. The tendons in middle MTP joint are mainly used to transfer force and withstand the pressure from the vertical direction of tendons. In lower end of MTP joint, the tendons have to connect phalanxes and reduce vibration, so both stiffness and wave structure of it are small. Moreover, a large number of collagen filaments distributed between the fiber bundles play roles in force transfer, connecting fiber bundle and preventing tear and so on.To investigate the effect of ostrich foot movement on energy storage and vibration reduction, Simi Motion capture and analysis system was utilized to measure the movement of ostrich on two different media with different gait, meanwhile, foot pressure plate and Footscan software were involved to record and analyze the foot pressure distribution of ostrich and its variation. The experiment result indicated that,despite difference of road surface and gait, the front or middle digit Ⅲ of ostrich foot firstly contact with the ground without impact vibration. With MTP joint moving down, the angle of MTP joint continuously decreased and the foot pressure continuously increased. Later, with MTP joint moving up, the angle of MTP joint increased and the foot pressure decreased. Throughout the touchdown, the digit Ⅲundertook more than 70% of load and played the biggest role in vibration reduction.Combined the kinematics data and plantar pressure data, the potential energy of MTP joint can be calculated, which increased in early touchdown and decreased later. In the same road surface, the maximum potential energy of MTP joint was larger in running than that in walking. In running, the maximum potential energy in MTP joint was bigger in hard load surface than that in sand road, but the load surface has little impact on potential energy accumulation of MTP joint.Based on the mechanism of energy storage and vibration reduction of ostrich MTP joint, a vibration reduction and self-adaption bionic walking-wheel foot was designed by the engineering bionic method. The Finite Element Numerical Simulation and soil-bin test were performed to analyze the performance of bionic walking-wheel foot. The result showed that wheel center fluctuation of the bionic walking-wheel was less than that of traditional walking-wheel, and the vibration of wheel center reduced obviously in bionic walking-wheel.